[Xen-devel] [PATCH v10 0/9] error: auto propagated local_err part I

[Xen-devel] [PATCH v10 0/9] error: auto propagated local_err part I

[Vladimir Sementsov-Ogievskiy]

v10: (based-on "[PATCH 0/3] Minor error handling cleanups" including my 4/3 in it)
02: Change some comments.
    Do not chain check1 and check2 rules to rule1 to cover move
    unusual cases to warn about.
    Add positions to check1 rule.
    Move check1 and check2 above rule1, otherwise our ___ hack will break check2
    rule.
03: add hunk, due to rebasing and
09: rebased. Change is trivial, I keep r-b.


v10 is available at
 https://src.openvz.org/scm/~vsementsov/qemu.git #tag up-auto-local-err-partI-v10
v9 is available at
 https://src.openvz.org/scm/~vsementsov/qemu.git #tag up-auto-local-err-partI-v9


In these series, there is no commit-per-subsystem script, each generated
commit is generated in separate.

Still, generating commands are very similar, and looks like

    sed -n '/^<Subsystem name>$/,/^$/{s/^F: //p}' MAINTAINERS | \
    xargs git ls-files | grep '\.[hc]$' | \
    xargs spatch \
        --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
        --macro-file scripts/cocci-macro-file.h \
        --in-place --no-show-diff --max-width 80

Note, that in each generated commit, generation command is the only
text, indented by 8 spaces in 'git log -1' output, so, to regenerate all
commits (for example, after rebase, or change in coccinelle script), you
may use the following command:

git rebase -x "sh -c \"git show --pretty= --name-only | xargs git checkout HEAD^ -- ; git reset; git log -1 | grep '^        ' | sh\"" HEAD~7

Which will start automated interactive rebase for generated patches,
which will stop if generated patch changed
(you may do git commit --amend to apply updated generated changes).

Note:
  git show --pretty= --name-only   - lists files, changed in HEAD
  git log -1 | grep '^        ' | sh   - rerun generation command of HEAD


Check for compilation of changed .c files
git rebase -x "sh -c \"git show --pretty= --name-only | sed -n 's/\.c$/.o/p' | xargs make -j9\"" HEAD~7

Vladimir Sementsov-Ogievskiy (9):
  error: auto propagated local_err
  scripts: Coccinelle script to use ERRP_AUTO_PROPAGATE()
  SD (Secure Card): introduce ERRP_AUTO_PROPAGATE
  pflash: introduce ERRP_AUTO_PROPAGATE
  fw_cfg: introduce ERRP_AUTO_PROPAGATE
  virtio-9p: introduce ERRP_AUTO_PROPAGATE
  TPM: introduce ERRP_AUTO_PROPAGATE
  nbd: introduce ERRP_AUTO_PROPAGATE
  xen: introduce ERRP_AUTO_PROPAGATE

 scripts/coccinelle/auto-propagated-errp.cocci | 336 ++++++++++++++++++
 include/block/nbd.h                           |   1 +
 include/qapi/error.h                          | 208 +++++++++--
 block/nbd.c                                   |  21 +-
 hw/9pfs/9p-local.c                            |  12 +-
 hw/9pfs/9p.c                                  |   1 +
 hw/block/dataplane/xen-block.c                |  17 +-
 hw/block/pflash_cfi01.c                       |   7 +-
 hw/block/pflash_cfi02.c                       |   7 +-
 hw/block/xen-block.c                          | 122 +++----
 hw/nvram/fw_cfg.c                             |  14 +-
 hw/pci-host/xen_igd_pt.c                      |   7 +-
 hw/sd/sdhci-pci.c                             |   7 +-
 hw/sd/sdhci.c                                 |  21 +-
 hw/sd/ssi-sd.c                                |  16 +-
 hw/tpm/tpm_util.c                             |   7 +-
 hw/xen/xen-backend.c                          |   7 +-
 hw/xen/xen-bus.c                              |  92 ++---
 hw/xen/xen-host-pci-device.c                  |  27 +-
 hw/xen/xen_pt.c                               |  25 +-
 hw/xen/xen_pt_config_init.c                   |  20 +-
 nbd/client.c                                  |   5 +
 nbd/server.c                                  |   5 +
 tpm.c                                         |   7 +-
 MAINTAINERS                                   |   1 +
 25 files changed, 715 insertions(+), 278 deletions(-)
 create mode 100644 scripts/coccinelle/auto-propagated-errp.cocci

Cc: Eric Blake <eblake@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Greg Kurz <groug@kaod.org>
Cc: Christian Schoenebeck <qemu_oss@crudebyte.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Paul Durrant <paul@xen.org>
Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Stefan Berger <stefanb@linux.ibm.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Michael Roth <mdroth@linux.vnet.ibm.com>
Cc: qemu-devel@nongnu.org
Cc: qemu-block@nongnu.org
Cc: xen-devel@lists.xenproject.org

-- 
2.21.0


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

[Xen-devel] [PATCH v10 1/9] error: auto propagated local_err

[Vladimir Sementsov-Ogievskiy]

Introduce a new ERRP_AUTO_PROPAGATE macro, to be used at start of
functions with an errp OUT parameter.

It has three goals:

1. Fix issue with error_fatal and error_prepend/error_append_hint: user
can't see this additional information, because exit() happens in
error_setg earlier than information is added. [Reported by Greg Kurz]

2. Fix issue with error_abort and error_propagate: when we wrap
error_abort by local_err+error_propagate, the resulting coredump will
refer to error_propagate and not to the place where error happened.
(the macro itself doesn't fix the issue, but it allows us to [3.] drop
the local_err+error_propagate pattern, which will definitely fix the
issue) [Reported by Kevin Wolf]

3. Drop local_err+error_propagate pattern, which is used to workaround
void functions with errp parameter, when caller wants to know resulting
status. (Note: actually these functions could be merely updated to
return int error code).

To achieve these goals, later patches will add invocations
of this macro at the start of functions with either use
error_prepend/error_append_hint (solving 1) or which use
local_err+error_propagate to check errors, switching those
functions to use *errp instead (solving 2 and 3).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
---

Cc: Eric Blake <eblake@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Greg Kurz <groug@kaod.org>
Cc: Christian Schoenebeck <qemu_oss@crudebyte.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Paul Durrant <paul@xen.org>
Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Stefan Berger <stefanb@linux.ibm.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Michael Roth <mdroth@linux.vnet.ibm.com>
Cc: qemu-devel@nongnu.org
Cc: qemu-block@nongnu.org
Cc: xen-devel@lists.xenproject.org

 include/qapi/error.h | 205 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 173 insertions(+), 32 deletions(-)

diff --git a/include/qapi/error.h b/include/qapi/error.h
index ad5b6e896d..30140d9bfe 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -15,6 +15,8 @@
 /*
  * Error reporting system loosely patterned after Glib's GError.
  *
+ * = Deal with Error object =
+ *
  * Create an error:
  *     error_setg(&err, "situation normal, all fouled up");
  *
@@ -47,28 +49,91 @@
  * reporting it (primarily useful in testsuites):
  *     error_free_or_abort(&err);
  *
- * Pass an existing error to the caller:
- *     error_propagate(errp, err);
- * where Error **errp is a parameter, by convention the last one.
+ * = Deal with Error ** function parameter =
  *
- * Pass an existing error to the caller with the message modified:
- *     error_propagate_prepend(errp, err);
+ * A function may use the error system to return errors. In this case, the
+ * function defines an Error **errp parameter, by convention the last one (with
+ * exceptions for functions using ... or va_list).
  *
- * Avoid
- *     error_propagate(errp, err);
- *     error_prepend(errp, "Could not frobnicate '%s': ", name);
- * because this fails to prepend when @errp is &error_fatal.
+ * The caller may then pass in the following errp values:
  *
- * Create a new error and pass it to the caller:
+ * 1. &error_abort
+ *    Any error will result in abort().
+ * 2. &error_fatal
+ *    Any error will result in exit() with a non-zero status.
+ * 3. NULL
+ *    No error reporting through errp parameter.
+ * 4. The address of a NULL-initialized Error *err
+ *    Any error will populate errp with an error object.
+ *
+ * The following rules then implement the correct semantics desired by the
+ * caller.
+ *
+ * Create a new error to pass to the caller:
  *     error_setg(errp, "situation normal, all fouled up");
  *
- * Call a function and receive an error from it:
+ * Calling another errp-based function:
+ *     f(..., errp);
+ *
+ * == Checking success of subcall ==
+ *
+ * If a function returns a value indicating an error in addition to setting
+ * errp (which is recommended), then you don't need any additional code, just
+ * do:
+ *
+ *     int ret = f(..., errp);
+ *     if (ret < 0) {
+ *         ... handle error ...
+ *         return ret;
+ *     }
+ *
+ * If a function returns nothing (not recommended for new code), the only way
+ * to check success is by consulting errp; doing this safely requires the use
+ * of the ERRP_AUTO_PROPAGATE macro, like this:
+ *
+ *     int our_func(..., Error **errp) {
+ *         ERRP_AUTO_PROPAGATE();
+ *         ...
+ *         subcall(..., errp);
+ *         if (*errp) {
+ *             ...
+ *             return -EINVAL;
+ *         }
+ *         ...
+ *     }
+ *
+ * ERRP_AUTO_PROPAGATE takes care of wrapping the original errp as needed, so
+ * that the rest of the function can directly use errp (including
+ * dereferencing), where any errors will then be propagated on to the original
+ * errp when leaving the function.
+ *
+ * In some cases, we need to check result of subcall, but do not want to
+ * propagate the Error object to our caller. In such cases we don't need
+ * ERRP_AUTO_PROPAGATE, but just a local Error object:
+ *
+ * Receive an error and not pass it:
  *     Error *err = NULL;
- *     foo(arg, &err);
+ *     subcall(arg, &err);
  *     if (err) {
  *         handle the error...
+ *         error_free(err);
  *     }
  *
+ * Note that older code that did not use ERRP_AUTO_PROPAGATE would instead need
+ * a local Error * variable and the use of error_propagate() to properly handle
+ * all possible caller values of errp. Now this is DEPRECATED* (see below).
+ *
+ * Note that any function that wants to modify an error object, such as by
+ * calling error_append_hint or error_prepend, must use ERRP_AUTO_PROPAGATE, in
+ * order for a caller's use of &error_fatal to see the additional information.
+ *
+ * In rare cases, we need to pass existing Error object to the caller by hand:
+ *     error_propagate(errp, err);
+ *
+ * Pass an existing error to the caller with the message modified:
+ *     error_propagate_prepend(errp, err);
+ *
+ *
  * Call a function ignoring errors:
  *     foo(arg, NULL);
  *
@@ -78,26 +143,6 @@
  * Call a function treating errors as fatal:
  *     foo(arg, &error_fatal);
  *
- * Receive an error and pass it on to the caller:
- *     Error *err = NULL;
- *     foo(arg, &err);
- *     if (err) {
- *         handle the error...
- *         error_propagate(errp, err);
- *     }
- * where Error **errp is a parameter, by convention the last one.
- *
- * Do *not* "optimize" this to
- *     foo(arg, errp);
- *     if (*errp) { // WRONG!
- *         handle the error...
- *     }
- * because errp may be NULL!
- *
- * But when all you do with the error is pass it on, please use
- *     foo(arg, errp);
- * for readability.
- *
  * Receive and accumulate multiple errors (first one wins):
  *     Error *err = NULL, *local_err = NULL;
  *     foo(arg, &err);
@@ -114,6 +159,61 @@
  *         handle the error...
  *     }
  * because this may pass a non-null err to bar().
+ *
+ * DEPRECATED*
+ *
+ * The following pattern of receiving, checking, and then forwarding an error
+ * to the caller by hand is now deprecated:
+ *
+ *     Error *err = NULL;
+ *     foo(arg, &err);
+ *     if (err) {
+ *         handle the error...
+ *         error_propagate(errp, err);
+ *     }
+ *
+ * Instead, use ERRP_AUTO_PROPAGATE macro.
+ *
+ * The old pattern is deprecated because of two things:
+ *
+ * 1. Issue with error_abort and error_propagate: when we wrap error_abort by
+ * local_err+error_propagate, the resulting coredump will refer to
+ * error_propagate and not to the place where error happened.
+ *
+ * 2. A lot of extra code of the same pattern
+ *
+ * How to update old code to use ERRP_AUTO_PROPAGATE?
+ *
+ * All you need is to add ERRP_AUTO_PROPAGATE() invocation at function start,
+ * than you may safely dereference errp to check errors and do not need any
+ * additional local Error variables or calls to error_propagate().
+ *
+ * Example:
+ *
+ * old code
+ *
+ *     void fn(..., Error **errp) {
+ *         Error *err = NULL;
+ *         foo(arg, &err);
+ *         if (err) {
+ *             handle the error...
+ *             error_propagate(errp, err);
+ *             return;
+ *         }
+ *         ...
+ *     }
+ *
+ * updated code
+ *
+ *     void fn(..., Error **errp) {
+ *         ERRP_AUTO_PROPAGATE();
+ *         foo(arg, errp);
+ *         if (*errp) {
+ *             handle the error...
+ *             return;
+ *         }
+ *         ...
+ *     }
  */
 
 #ifndef ERROR_H
@@ -322,6 +422,47 @@ void error_set_internal(Error **errp,
                         ErrorClass err_class, const char *fmt, ...)
     GCC_FMT_ATTR(6, 7);
 
+typedef struct ErrorPropagator {
+    Error *local_err;
+    Error **errp;
+} ErrorPropagator;
+
+static inline void error_propagator_cleanup(ErrorPropagator *prop)
+{
+    error_propagate(prop->errp, prop->local_err);
+}
+
+G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagator, error_propagator_cleanup);
+
+/*
+ * ERRP_AUTO_PROPAGATE
+ *
+ * This macro exists to assist with proper error handling in a function which
+ * uses an Error **errp parameter.  It must be used as the first line of a
+ * function which modifies an error (with error_prepend, error_append_hint, or
+ * similar) or which wants to dereference *errp.  It is still safe (but
+ * useless) to use in other functions.
+ *
+ * If errp is NULL or points to error_fatal, it is rewritten to point to a
+ * local Error object, which will be automatically propagated to the original
+ * errp on function exit (see error_propagator_cleanup).
+ *
+ * After invocation of this macro it is always safe to dereference errp
+ * (as it's not NULL anymore) and to add information by error_prepend or
+ * error_append_hint (as, if it was error_fatal, we swapped it with a
+ * local_error to be propagated on cleanup).
+ *
+ * Note: we don't wrap the error_abort case, as we want resulting coredump
+ * to point to the place where the error happened, not to error_propagate.
+ */
+#define ERRP_AUTO_PROPAGATE() \
+    g_auto(ErrorPropagator) _auto_errp_prop = {.errp = errp}; \
+    do { \
+        if (!errp || errp == &error_fatal) { \
+            errp = &_auto_errp_prop.local_err; \
+        } \
+    } while (0)
+
 /*
  * Special error destination to abort on error.
  * See error_setg() and error_propagate() for details.
-- 
2.21.0


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

Re: [PATCH v10 1/9] error: auto propagated local_err

[Greg Kurz]

On Tue, 17 Mar 2020 18:16:17 +0300
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:

> Introduce a new ERRP_AUTO_PROPAGATE macro, to be used at start of
> functions with an errp OUT parameter.
> 
> It has three goals:
> 
> 1. Fix issue with error_fatal and error_prepend/error_append_hint: user
> can't see this additional information, because exit() happens in
> error_setg earlier than information is added. [Reported by Greg Kurz]
> 

I have more of these coming and I'd really like to use ERRP_AUTO_PROPAGATE.

It seems we have a consensus on the macro itself but this series is gated
by the conversion of the existing code base.

What about merging this patch separately so that people can start using
it at least ?

> 2. Fix issue with error_abort and error_propagate: when we wrap
> error_abort by local_err+error_propagate, the resulting coredump will
> refer to error_propagate and not to the place where error happened.
> (the macro itself doesn't fix the issue, but it allows us to [3.] drop
> the local_err+error_propagate pattern, which will definitely fix the
> issue) [Reported by Kevin Wolf]
> 
> 3. Drop local_err+error_propagate pattern, which is used to workaround
> void functions with errp parameter, when caller wants to know resulting
> status. (Note: actually these functions could be merely updated to
> return int error code).
> 
> To achieve these goals, later patches will add invocations
> of this macro at the start of functions with either use
> error_prepend/error_append_hint (solving 1) or which use
> local_err+error_propagate to check errors, switching those
> functions to use *errp instead (solving 2 and 3).
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Reviewed-by: Paul Durrant <paul@xen.org>
> Reviewed-by: Greg Kurz <groug@kaod.org>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
> 
> Cc: Eric Blake <eblake@redhat.com>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Max Reitz <mreitz@redhat.com>
> Cc: Greg Kurz <groug@kaod.org>
> Cc: Christian Schoenebeck <qemu_oss@crudebyte.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Anthony Perard <anthony.perard@citrix.com>
> Cc: Paul Durrant <paul@xen.org>
> Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Stefan Berger <stefanb@linux.ibm.com>
> Cc: Markus Armbruster <armbru@redhat.com>
> Cc: Michael Roth <mdroth@linux.vnet.ibm.com>
> Cc: qemu-devel@nongnu.org
> Cc: qemu-block@nongnu.org
> Cc: xen-devel@lists.xenproject.org
> 
>  include/qapi/error.h | 205 ++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 173 insertions(+), 32 deletions(-)
> 
> diff --git a/include/qapi/error.h b/include/qapi/error.h
> index ad5b6e896d..30140d9bfe 100644
> --- a/include/qapi/error.h
> +++ b/include/qapi/error.h
> @@ -15,6 +15,8 @@
>  /*
>   * Error reporting system loosely patterned after Glib's GError.
>   *
> + * = Deal with Error object =
> + *
>   * Create an error:
>   *     error_setg(&err, "situation normal, all fouled up");
>   *
> @@ -47,28 +49,91 @@
>   * reporting it (primarily useful in testsuites):
>   *     error_free_or_abort(&err);
>   *
> - * Pass an existing error to the caller:
> - *     error_propagate(errp, err);
> - * where Error **errp is a parameter, by convention the last one.
> + * = Deal with Error ** function parameter =
>   *
> - * Pass an existing error to the caller with the message modified:
> - *     error_propagate_prepend(errp, err);
> + * A function may use the error system to return errors. In this case, the
> + * function defines an Error **errp parameter, by convention the last one (with
> + * exceptions for functions using ... or va_list).
>   *
> - * Avoid
> - *     error_propagate(errp, err);
> - *     error_prepend(errp, "Could not frobnicate '%s': ", name);
> - * because this fails to prepend when @errp is &error_fatal.
> + * The caller may then pass in the following errp values:
>   *
> - * Create a new error and pass it to the caller:
> + * 1. &error_abort
> + *    Any error will result in abort().
> + * 2. &error_fatal
> + *    Any error will result in exit() with a non-zero status.
> + * 3. NULL
> + *    No error reporting through errp parameter.
> + * 4. The address of a NULL-initialized Error *err
> + *    Any error will populate errp with an error object.
> + *
> + * The following rules then implement the correct semantics desired by the
> + * caller.
> + *
> + * Create a new error to pass to the caller:
>   *     error_setg(errp, "situation normal, all fouled up");
>   *
> - * Call a function and receive an error from it:
> + * Calling another errp-based function:
> + *     f(..., errp);
> + *
> + * == Checking success of subcall ==
> + *
> + * If a function returns a value indicating an error in addition to setting
> + * errp (which is recommended), then you don't need any additional code, just
> + * do:
> + *
> + *     int ret = f(..., errp);
> + *     if (ret < 0) {
> + *         ... handle error ...
> + *         return ret;
> + *     }
> + *
> + * If a function returns nothing (not recommended for new code), the only way
> + * to check success is by consulting errp; doing this safely requires the use
> + * of the ERRP_AUTO_PROPAGATE macro, like this:
> + *
> + *     int our_func(..., Error **errp) {
> + *         ERRP_AUTO_PROPAGATE();
> + *         ...
> + *         subcall(..., errp);
> + *         if (*errp) {
> + *             ...
> + *             return -EINVAL;
> + *         }
> + *         ...
> + *     }
> + *
> + * ERRP_AUTO_PROPAGATE takes care of wrapping the original errp as needed, so
> + * that the rest of the function can directly use errp (including
> + * dereferencing), where any errors will then be propagated on to the original
> + * errp when leaving the function.
> + *
> + * In some cases, we need to check result of subcall, but do not want to
> + * propagate the Error object to our caller. In such cases we don't need
> + * ERRP_AUTO_PROPAGATE, but just a local Error object:
> + *
> + * Receive an error and not pass it:
>   *     Error *err = NULL;
> - *     foo(arg, &err);
> + *     subcall(arg, &err);
>   *     if (err) {
>   *         handle the error...
> + *         error_free(err);
>   *     }
>   *
> + * Note that older code that did not use ERRP_AUTO_PROPAGATE would instead need
> + * a local Error * variable and the use of error_propagate() to properly handle
> + * all possible caller values of errp. Now this is DEPRECATED* (see below).
> + *
> + * Note that any function that wants to modify an error object, such as by
> + * calling error_append_hint or error_prepend, must use ERRP_AUTO_PROPAGATE, in
> + * order for a caller's use of &error_fatal to see the additional information.
> + *
> + * In rare cases, we need to pass existing Error object to the caller by hand:
> + *     error_propagate(errp, err);
> + *
> + * Pass an existing error to the caller with the message modified:
> + *     error_propagate_prepend(errp, err);
> + *
> + *
>   * Call a function ignoring errors:
>   *     foo(arg, NULL);
>   *
> @@ -78,26 +143,6 @@
>   * Call a function treating errors as fatal:
>   *     foo(arg, &error_fatal);
>   *
> - * Receive an error and pass it on to the caller:
> - *     Error *err = NULL;
> - *     foo(arg, &err);
> - *     if (err) {
> - *         handle the error...
> - *         error_propagate(errp, err);
> - *     }
> - * where Error **errp is a parameter, by convention the last one.
> - *
> - * Do *not* "optimize" this to
> - *     foo(arg, errp);
> - *     if (*errp) { // WRONG!
> - *         handle the error...
> - *     }
> - * because errp may be NULL!
> - *
> - * But when all you do with the error is pass it on, please use
> - *     foo(arg, errp);
> - * for readability.
> - *
>   * Receive and accumulate multiple errors (first one wins):
>   *     Error *err = NULL, *local_err = NULL;
>   *     foo(arg, &err);
> @@ -114,6 +159,61 @@
>   *         handle the error...
>   *     }
>   * because this may pass a non-null err to bar().
> + *
> + * DEPRECATED*
> + *
> + * The following pattern of receiving, checking, and then forwarding an error
> + * to the caller by hand is now deprecated:
> + *
> + *     Error *err = NULL;
> + *     foo(arg, &err);
> + *     if (err) {
> + *         handle the error...
> + *         error_propagate(errp, err);
> + *     }
> + *
> + * Instead, use ERRP_AUTO_PROPAGATE macro.
> + *
> + * The old pattern is deprecated because of two things:
> + *
> + * 1. Issue with error_abort and error_propagate: when we wrap error_abort by
> + * local_err+error_propagate, the resulting coredump will refer to
> + * error_propagate and not to the place where error happened.
> + *
> + * 2. A lot of extra code of the same pattern
> + *
> + * How to update old code to use ERRP_AUTO_PROPAGATE?
> + *
> + * All you need is to add ERRP_AUTO_PROPAGATE() invocation at function start,
> + * than you may safely dereference errp to check errors and do not need any
> + * additional local Error variables or calls to error_propagate().
> + *
> + * Example:
> + *
> + * old code
> + *
> + *     void fn(..., Error **errp) {
> + *         Error *err = NULL;
> + *         foo(arg, &err);
> + *         if (err) {
> + *             handle the error...
> + *             error_propagate(errp, err);
> + *             return;
> + *         }
> + *         ...
> + *     }
> + *
> + * updated code
> + *
> + *     void fn(..., Error **errp) {
> + *         ERRP_AUTO_PROPAGATE();
> + *         foo(arg, errp);
> + *         if (*errp) {
> + *             handle the error...
> + *             return;
> + *         }
> + *         ...
> + *     }
>   */
>  
>  #ifndef ERROR_H
> @@ -322,6 +422,47 @@ void error_set_internal(Error **errp,
>                          ErrorClass err_class, const char *fmt, ...)
>      GCC_FMT_ATTR(6, 7);
>  
> +typedef struct ErrorPropagator {
> +    Error *local_err;
> +    Error **errp;
> +} ErrorPropagator;
> +
> +static inline void error_propagator_cleanup(ErrorPropagator *prop)
> +{
> +    error_propagate(prop->errp, prop->local_err);
> +}
> +
> +G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagator, error_propagator_cleanup);
> +
> +/*
> + * ERRP_AUTO_PROPAGATE
> + *
> + * This macro exists to assist with proper error handling in a function which
> + * uses an Error **errp parameter.  It must be used as the first line of a
> + * function which modifies an error (with error_prepend, error_append_hint, or
> + * similar) or which wants to dereference *errp.  It is still safe (but
> + * useless) to use in other functions.
> + *
> + * If errp is NULL or points to error_fatal, it is rewritten to point to a
> + * local Error object, which will be automatically propagated to the original
> + * errp on function exit (see error_propagator_cleanup).
> + *
> + * After invocation of this macro it is always safe to dereference errp
> + * (as it's not NULL anymore) and to add information by error_prepend or
> + * error_append_hint (as, if it was error_fatal, we swapped it with a
> + * local_error to be propagated on cleanup).
> + *
> + * Note: we don't wrap the error_abort case, as we want resulting coredump
> + * to point to the place where the error happened, not to error_propagate.
> + */
> +#define ERRP_AUTO_PROPAGATE() \
> +    g_auto(ErrorPropagator) _auto_errp_prop = {.errp = errp}; \
> +    do { \
> +        if (!errp || errp == &error_fatal) { \
> +            errp = &_auto_errp_prop.local_err; \
> +        } \
> +    } while (0)
> +
>  /*
>   * Special error destination to abort on error.
>   * See error_setg() and error_propagate() for details.

Re: [PATCH v10 1/9] error: auto propagated local_err

[Markus Armbruster]

Greg Kurz <groug@kaod.org> writes:

> On Tue, 17 Mar 2020 18:16:17 +0300
> Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:
>
>> Introduce a new ERRP_AUTO_PROPAGATE macro, to be used at start of
>> functions with an errp OUT parameter.
>> 
>> It has three goals:
>> 
>> 1. Fix issue with error_fatal and error_prepend/error_append_hint: user
>> can't see this additional information, because exit() happens in
>> error_setg earlier than information is added. [Reported by Greg Kurz]
>> 
>
> I have more of these coming and I'd really like to use ERRP_AUTO_PROPAGATE.
>
> It seems we have a consensus on the macro itself but this series is gated
> by the conversion of the existing code base.
>
> What about merging this patch separately so that people can start using
> it at least ?

Please give me a few more days to finish the work I feel should go in
before the conversion.  With any luck, Vladimir can then rebase /
recreate the conversion easily, and you can finally use the macro for
your own work.

Re: [PATCH v10 1/9] error: auto propagated local_err

[Greg Kurz]

On Mon, 15 Jun 2020 07:21:03 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Greg Kurz <groug@kaod.org> writes:
> 
> > On Tue, 17 Mar 2020 18:16:17 +0300
> > Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:
> >
> >> Introduce a new ERRP_AUTO_PROPAGATE macro, to be used at start of
> >> functions with an errp OUT parameter.
> >> 
> >> It has three goals:
> >> 
> >> 1. Fix issue with error_fatal and error_prepend/error_append_hint: user
> >> can't see this additional information, because exit() happens in
> >> error_setg earlier than information is added. [Reported by Greg Kurz]
> >> 
> >
> > I have more of these coming and I'd really like to use ERRP_AUTO_PROPAGATE.
> >
> > It seems we have a consensus on the macro itself but this series is gated
> > by the conversion of the existing code base.
> >
> > What about merging this patch separately so that people can start using
> > it at least ?
> 
> Please give me a few more days to finish the work I feel should go in
> before the conversion.  With any luck, Vladimir can then rebase /
> recreate the conversion easily, and you can finally use the macro for
> your own work.
> 

Sure. Thanks.

Re: [PATCH v10 1/9] error: auto propagated local_err

[Markus Armbruster]

Greg Kurz <groug@kaod.org> writes:

> On Mon, 15 Jun 2020 07:21:03 +0200
> Markus Armbruster <armbru@redhat.com> wrote:
>
>> Greg Kurz <groug@kaod.org> writes:
>> 
>> > On Tue, 17 Mar 2020 18:16:17 +0300
>> > Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:
>> >
>> >> Introduce a new ERRP_AUTO_PROPAGATE macro, to be used at start of
>> >> functions with an errp OUT parameter.
>> >> 
>> >> It has three goals:
>> >> 
>> >> 1. Fix issue with error_fatal and error_prepend/error_append_hint: user
>> >> can't see this additional information, because exit() happens in
>> >> error_setg earlier than information is added. [Reported by Greg Kurz]
>> >> 
>> >
>> > I have more of these coming and I'd really like to use ERRP_AUTO_PROPAGATE.
>> >
>> > It seems we have a consensus on the macro itself but this series is gated
>> > by the conversion of the existing code base.
>> >
>> > What about merging this patch separately so that people can start using
>> > it at least ?
>> 
>> Please give me a few more days to finish the work I feel should go in
>> before the conversion.  With any luck, Vladimir can then rebase /
>> recreate the conversion easily, and you can finally use the macro for
>> your own work.
>> 
>
> Sure. Thanks.

Just posted "[PATCH 00/46] Less clumsy error checking".  The sheer size
of the thing and the length of its dependency chain explains why it took
me so long.  I feel bad about delaying you all the same.  Apologies!

I hope we can converge quickly enough to get Vladimir's work on top
ready in time for the soft freeze.

Re: [PATCH v10 1/9] error: auto propagated local_err

[Greg Kurz]

On Wed, 24 Jun 2020 18:53:05 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Greg Kurz <groug@kaod.org> writes:
> 
> > On Mon, 15 Jun 2020 07:21:03 +0200
> > Markus Armbruster <armbru@redhat.com> wrote:
> >
> >> Greg Kurz <groug@kaod.org> writes:
> >> 
> >> > On Tue, 17 Mar 2020 18:16:17 +0300
> >> > Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:
> >> >
> >> >> Introduce a new ERRP_AUTO_PROPAGATE macro, to be used at start of
> >> >> functions with an errp OUT parameter.
> >> >> 
> >> >> It has three goals:
> >> >> 
> >> >> 1. Fix issue with error_fatal and error_prepend/error_append_hint: user
> >> >> can't see this additional information, because exit() happens in
> >> >> error_setg earlier than information is added. [Reported by Greg Kurz]
> >> >> 
> >> >
> >> > I have more of these coming and I'd really like to use ERRP_AUTO_PROPAGATE.
> >> >
> >> > It seems we have a consensus on the macro itself but this series is gated
> >> > by the conversion of the existing code base.
> >> >
> >> > What about merging this patch separately so that people can start using
> >> > it at least ?
> >> 
> >> Please give me a few more days to finish the work I feel should go in
> >> before the conversion.  With any luck, Vladimir can then rebase /
> >> recreate the conversion easily, and you can finally use the macro for
> >> your own work.
> >> 
> >
> > Sure. Thanks.
> 
> Just posted "[PATCH 00/46] Less clumsy error checking".  The sheer size
> of the thing and the length of its dependency chain explains why it took
> me so long.  I feel bad about delaying you all the same.  Apologies!
> 

No problem. This series of yours is impressive. Putting an end to the
highjacking of the Error ** argument is really a beneficial move.

> I hope we can converge quickly enough to get Vladimir's work on top
> ready in time for the soft freeze.
> 

I'll find some cycles for reviewing.

Cheers,

--
Greg

[Xen-devel] [PATCH v10 2/9] scripts: Coccinelle script to use ERRP_AUTO_PROPAGATE()

[Vladimir Sementsov-Ogievskiy]

Script adds ERRP_AUTO_PROPAGATE macro invocation where appropriate and
does corresponding changes in code (look for details in
include/qapi/error.h)

Usage example:
spatch --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
 --macro-file scripts/cocci-macro-file.h --in-place --no-show-diff \
 --max-width 80 FILES...

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---

Cc: Eric Blake <eblake@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Greg Kurz <groug@kaod.org>
Cc: Christian Schoenebeck <qemu_oss@crudebyte.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Paul Durrant <paul@xen.org>
Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Stefan Berger <stefanb@linux.ibm.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Michael Roth <mdroth@linux.vnet.ibm.com>
Cc: qemu-devel@nongnu.org
Cc: qemu-block@nongnu.org
Cc: xen-devel@lists.xenproject.org

 scripts/coccinelle/auto-propagated-errp.cocci | 336 ++++++++++++++++++
 include/qapi/error.h                          |   3 +
 MAINTAINERS                                   |   1 +
 3 files changed, 340 insertions(+)
 create mode 100644 scripts/coccinelle/auto-propagated-errp.cocci

diff --git a/scripts/coccinelle/auto-propagated-errp.cocci b/scripts/coccinelle/auto-propagated-errp.cocci
new file mode 100644
index 0000000000..5188b07006
--- /dev/null
+++ b/scripts/coccinelle/auto-propagated-errp.cocci
@@ -0,0 +1,336 @@
+// Use ERRP_AUTO_PROPAGATE (see include/qapi/error.h)
+//
+// Copyright (c) 2020 Virtuozzo International GmbH.
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see
+// <http://www.gnu.org/licenses/>.
+//
+// Usage example:
+// spatch --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
+//  --macro-file scripts/cocci-macro-file.h --in-place \
+//  --no-show-diff --max-width 80 FILES...
+//
+// Note: --max-width 80 is needed because coccinelle default is less
+// than 80, and without this parameter coccinelle may reindent some
+// lines which fit into 80 characters but not to coccinelle default,
+// which in turn produces extra patch hunks for no reason.
+
+// Switch unusual Error ** parameter names to errp
+// (this is necessary to use ERRP_AUTO_PROPAGATE).
+//
+// Disable optional_qualifier to skip functions with
+// "Error *const *errp" parameter.
+//
+// Skip functions with "assert(_errp && *_errp)" statement, because
+// that signals unusual semantics, and the parameter name may well
+// serve a purpose. (like nbd_iter_channel_error()).
+//
+// Skip util/error.c to not touch, for example, error_propagate() and
+// error_propagate_prepend().
+@ depends on !(file in "util/error.c") disable optional_qualifier@
+identifier fn;
+identifier _errp != errp;
+@@
+
+ fn(...,
+-   Error **_errp
++   Error **errp
+    ,...)
+ {
+(
+     ... when != assert(_errp && *_errp)
+&
+     <...
+-    _errp
++    errp
+     ...>
+)
+ }
+
+// Add invocation of ERRP_AUTO_PROPAGATE to errp-functions where
+// necessary
+//
+// Note, that without "when any" the final "..." does not mach
+// something matched by previous pattern, i.e. the rule will not match
+// double error_prepend in control flow like in
+// vfio_set_irq_signaling().
+//
+// Note, "exists" says that we want apply rule even if it does not
+// match on all possible control flows (otherwise, it will not match
+// standard pattern when error_propagate() call is in if branch).
+@ disable optional_qualifier exists@
+identifier fn, local_err;
+symbol errp;
+@@
+
+ fn(..., Error **errp, ...)
+ {
++   ERRP_AUTO_PROPAGATE();
+    ...  when != ERRP_AUTO_PROPAGATE();
+(
+(
+    error_append_hint(errp, ...);
+|
+    error_prepend(errp, ...);
+|
+    error_vprepend(errp, ...);
+)
+    ... when any
+|
+    Error *local_err = NULL;
+    ...
+(
+    error_propagate_prepend(errp, local_err, ...);
+|
+    error_propagate(errp, local_err);
+)
+    ...
+)
+ }
+
+// Warn when several Error * definitions are in the control flow.
+// This rule is not chained to rule1 and less restrictive, to cover more
+// functions to warn (even those we are not going to convert).
+//
+// Note, that even with one (or zero) Error * definition in the each
+// control flow we may have several (in total) Error * definitions in
+// the function. This case deserves attention too, but I don't see
+// simple way to match with help of coccinelle.
+@check1 disable optional_qualifier exists@
+identifier fn, _errp, local_err, local_err2;
+position p1, p2;
+@@
+
+ fn(..., Error **_errp, ...)
+ {
+     ...
+     Error *local_err = NULL;@p1
+     ... when any
+     Error *local_err2 = NULL;@p2
+     ... when any
+ }
+
+@ script:python @
+fn << check1.fn;
+p1 << check1.p1;
+p2 << check1.p2;
+@@
+
+print('Warning: function {} has several definitions of '
+      'Error * local variable: at {}:{} and then at {}:{}'.format(
+          fn, p1[0].file, p1[0].line, p2[0].file, p2[0].line))
+
+// Warn when several propagations are in the control flow.
+@check2 disable optional_qualifier exists@
+identifier fn, _errp;
+position p1, p2;
+@@
+
+ fn(..., Error **_errp, ...)
+ {
+     ...
+(
+     error_propagate_prepend(_errp, ...);@p1
+|
+     error_propagate(_errp, ...);@p1
+)
+     ...
+(
+     error_propagate_prepend(_errp, ...);@p2
+|
+     error_propagate(_errp, ...);@p2
+)
+     ... when any
+ }
+
+@ script:python @
+fn << check2.fn;
+p1 << check2.p1;
+p2 << check2.p2;
+@@
+
+print('Warning: function {} propagates to errp several times in '
+      'one control flow: at {}:{} and then at {}:{}'.format(
+          fn, p1[0].file, p1[0].line, p2[0].file, p2[0].line))
+
+// Match functions with propagation of local error to errp.
+// We want to refer these functions in several following rules, but I
+// don't know a proper way to inherit a function, not just its name
+// (to not match another functions with same name in following rules).
+// Not-proper way is as follows: rename errp parameter in functions
+// header and match it in following rules. Rename it back after all
+// transformations.
+//
+// The common case is a single definition of local_err with at most one
+// error_propagate_prepend() or error_propagate() on each control-flow
+// path. Functions with multiple definitions or propagates we want to
+// examine manually. Later rules emit warnings to guide us to them.
+//
+// Note that we match not only this "common case", but any function,
+// which has the "common cose" on at least one control-flow path.
+@rule1 disable optional_qualifier exists@
+identifier fn, local_err;
+symbol errp;
+@@
+
+ fn(..., Error **
+-    errp
++    ____
+    , ...)
+ {
+     ...
+     Error *local_err = NULL;
+     ...
+(
+     error_propagate_prepend(errp, local_err, ...);
+|
+     error_propagate(errp, local_err);
+)
+     ...
+ }
+
+// Convert special case with goto separately.
+// I tried merging this into the following rule the obvious way, but
+// it made Coccinelle hang on block.c
+//
+// Note interesting thing: if we don't do it here, and try to fixup
+// "out: }" things later after all transformations (the rule will be
+// the same, just without error_propagate() call), coccinelle fails to
+// match this "out: }".
+@ disable optional_qualifier@
+identifier rule1.fn, rule1.local_err, out;
+symbol errp;
+@@
+
+ fn(..., Error ** ____, ...)
+ {
+     <...
+-    goto out;
++    return;
+     ...>
+- out:
+-    error_propagate(errp, local_err);
+ }
+
+// Convert most of local_err related stuff.
+//
+// Note, that we inherit rule1.fn and rule1.local_err names, not
+// objects themselves. We may match something not related to the
+// pattern matched by rule1. For example, local_err may be defined with
+// the same name in different blocks inside one function, and in one
+// block follow the propagation pattern and in other block doesn't.
+//
+// Note also that errp-cleaning functions
+//   error_free_errp
+//   error_report_errp
+//   error_reportf_errp
+//   warn_report_errp
+//   warn_reportf_errp
+// are not yet implemented. They must call corresponding Error* -
+// freeing function and then set *errp to NULL, to avoid further
+// propagation to original errp (consider ERRP_AUTO_PROPAGATE in use).
+// For example, error_free_errp may look like this:
+//
+//    void error_free_errp(Error **errp)
+//    {
+//        error_free(*errp);
+//        *errp = NULL;
+//    }
+@ disable optional_qualifier exists@
+identifier rule1.fn, rule1.local_err;
+expression list args;
+symbol errp;
+@@
+
+ fn(..., Error ** ____, ...)
+ {
+     <...
+(
+-    Error *local_err = NULL;
+|
+
+// Convert error clearing functions
+(
+-    error_free(local_err);
++    error_free_errp(errp);
+|
+-    error_report_err(local_err);
++    error_report_errp(errp);
+|
+-    error_reportf_err(local_err, args);
++    error_reportf_errp(errp, args);
+|
+-    warn_report_err(local_err);
++    warn_report_errp(errp);
+|
+-    warn_reportf_err(local_err, args);
++    warn_reportf_errp(errp, args);
+)
+?-    local_err = NULL;
+
+|
+-    error_propagate_prepend(errp, local_err, args);
++    error_prepend(errp, args);
+|
+-    error_propagate(errp, local_err);
+|
+-    &local_err
++    errp
+)
+     ...>
+ }
+
+// Convert remaining local_err usage. For example, different kinds of
+// error checking in if conditionals. We can't merge this into
+// previous hunk, as this conflicts with other substitutions in it (at
+// least with "- local_err = NULL").
+@ disable optional_qualifier@
+identifier rule1.fn, rule1.local_err;
+symbol errp;
+@@
+
+ fn(..., Error ** ____, ...)
+ {
+     <...
+-    local_err
++    *errp
+     ...>
+ }
+
+// Always use the same pattern for checking error
+@ disable optional_qualifier@
+identifier rule1.fn;
+symbol errp;
+@@
+
+ fn(..., Error ** ____, ...)
+ {
+     <...
+-    *errp != NULL
++    *errp
+     ...>
+ }
+
+// Revert temporary ___ identifier.
+@ disable optional_qualifier@
+identifier rule1.fn;
+@@
+
+ fn(..., Error **
+-   ____
++   errp
+    , ...)
+ {
+     ...
+ }
diff --git a/include/qapi/error.h b/include/qapi/error.h
index 30140d9bfe..56c133520d 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -214,6 +214,9 @@
  *         }
  *         ...
  *     }
+ *
+ * For mass-conversion use script
+ *   scripts/coccinelle/auto-propagated-errp.cocci
  */
 
 #ifndef ERROR_H
diff --git a/MAINTAINERS b/MAINTAINERS
index 32867bc636..8b77127c35 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2016,6 +2016,7 @@ F: include/qemu/error-report.h
 F: qapi/error.json
 F: util/error.c
 F: util/qemu-error.c
+F: scripts/coccinelle/*err*.cocci
 
 GDB stub
 M: Alex Bennée <alex.bennee@linaro.org>
-- 
2.21.0


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Re: [Xen-devel] [PATCH v10 2/9] scripts: Coccinelle script to use ERRP_AUTO_PROPAGATE()

[Markus Armbruster]

Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:

> Script adds ERRP_AUTO_PROPAGATE macro invocation where appropriate and
> does corresponding changes in code (look for details in
> include/qapi/error.h)
>
> Usage example:
> spatch --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
>  --macro-file scripts/cocci-macro-file.h --in-place --no-show-diff \
>  --max-width 80 FILES...
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>
> Cc: Eric Blake <eblake@redhat.com>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Max Reitz <mreitz@redhat.com>
> Cc: Greg Kurz <groug@kaod.org>
> Cc: Christian Schoenebeck <qemu_oss@crudebyte.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Anthony Perard <anthony.perard@citrix.com>
> Cc: Paul Durrant <paul@xen.org>
> Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Stefan Berger <stefanb@linux.ibm.com>
> Cc: Markus Armbruster <armbru@redhat.com>
> Cc: Michael Roth <mdroth@linux.vnet.ibm.com>
> Cc: qemu-devel@nongnu.org
> Cc: qemu-block@nongnu.org
> Cc: xen-devel@lists.xenproject.org
>
>  scripts/coccinelle/auto-propagated-errp.cocci | 336 ++++++++++++++++++
>  include/qapi/error.h                          |   3 +
>  MAINTAINERS                                   |   1 +
>  3 files changed, 340 insertions(+)
>  create mode 100644 scripts/coccinelle/auto-propagated-errp.cocci
>
> diff --git a/scripts/coccinelle/auto-propagated-errp.cocci b/scripts/coccinelle/auto-propagated-errp.cocci
> new file mode 100644
> index 0000000000..5188b07006
> --- /dev/null
> +++ b/scripts/coccinelle/auto-propagated-errp.cocci
> @@ -0,0 +1,336 @@
> +// Use ERRP_AUTO_PROPAGATE (see include/qapi/error.h)
> +//
> +// Copyright (c) 2020 Virtuozzo International GmbH.
> +//
> +// This program is free software; you can redistribute it and/or
> +// modify it under the terms of the GNU General Public License as
> +// published by the Free Software Foundation; either version 2 of the
> +// License, or (at your option) any later version.
> +//
> +// This program is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +// GNU General Public License for more details.
> +//
> +// You should have received a copy of the GNU General Public License
> +// along with this program.  If not, see
> +// <http://www.gnu.org/licenses/>.
> +//
> +// Usage example:
> +// spatch --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
> +//  --macro-file scripts/cocci-macro-file.h --in-place \
> +//  --no-show-diff --max-width 80 FILES...
> +//
> +// Note: --max-width 80 is needed because coccinelle default is less
> +// than 80, and without this parameter coccinelle may reindent some
> +// lines which fit into 80 characters but not to coccinelle default,
> +// which in turn produces extra patch hunks for no reason.
> +
> +// Switch unusual Error ** parameter names to errp
> +// (this is necessary to use ERRP_AUTO_PROPAGATE).
> +//
> +// Disable optional_qualifier to skip functions with
> +// "Error *const *errp" parameter.
> +//
> +// Skip functions with "assert(_errp && *_errp)" statement, because
> +// that signals unusual semantics, and the parameter name may well
> +// serve a purpose. (like nbd_iter_channel_error()).
> +//
> +// Skip util/error.c to not touch, for example, error_propagate() and
> +// error_propagate_prepend().
> +@ depends on !(file in "util/error.c") disable optional_qualifier@
> +identifier fn;
> +identifier _errp != errp;
> +@@
> +
> + fn(...,
> +-   Error **_errp
> ++   Error **errp
> +    ,...)
> + {
> +(
> +     ... when != assert(_errp && *_errp)
> +&
> +     <...
> +-    _errp
> ++    errp
> +     ...>
> +)
> + }
> +
> +// Add invocation of ERRP_AUTO_PROPAGATE to errp-functions where
> +// necessary
> +//
> +// Note, that without "when any" the final "..." does not mach
> +// something matched by previous pattern, i.e. the rule will not match
> +// double error_prepend in control flow like in
> +// vfio_set_irq_signaling().
> +//
> +// Note, "exists" says that we want apply rule even if it does not
> +// match on all possible control flows (otherwise, it will not match
> +// standard pattern when error_propagate() call is in if branch).
> +@ disable optional_qualifier exists@
> +identifier fn, local_err;
> +symbol errp;
> +@@
> +
> + fn(..., Error **errp, ...)
> + {
> ++   ERRP_AUTO_PROPAGATE();
> +    ...  when != ERRP_AUTO_PROPAGATE();
> +(
> +(
> +    error_append_hint(errp, ...);
> +|
> +    error_prepend(errp, ...);
> +|
> +    error_vprepend(errp, ...);
> +)
> +    ... when any
> +|
> +    Error *local_err = NULL;
> +    ...
> +(
> +    error_propagate_prepend(errp, local_err, ...);
> +|
> +    error_propagate(errp, local_err);
> +)
> +    ...
> +)
> + }
> +
> +// Warn when several Error * definitions are in the control flow.
> +// This rule is not chained to rule1 and less restrictive, to cover more
> +// functions to warn (even those we are not going to convert).
> +//
> +// Note, that even with one (or zero) Error * definition in the each
> +// control flow we may have several (in total) Error * definitions in
> +// the function. This case deserves attention too, but I don't see
> +// simple way to match with help of coccinelle.
> +@check1 disable optional_qualifier exists@
> +identifier fn, _errp, local_err, local_err2;
> +position p1, p2;
> +@@
> +
> + fn(..., Error **_errp, ...)
> + {
> +     ...
> +     Error *local_err = NULL;@p1
> +     ... when any
> +     Error *local_err2 = NULL;@p2
> +     ... when any
> + }
> +
> +@ script:python @
> +fn << check1.fn;
> +p1 << check1.p1;
> +p2 << check1.p2;
> +@@
> +
> +print('Warning: function {} has several definitions of '
> +      'Error * local variable: at {}:{} and then at {}:{}'.format(
> +          fn, p1[0].file, p1[0].line, p2[0].file, p2[0].line))
> +
> +// Warn when several propagations are in the control flow.
> +@check2 disable optional_qualifier exists@
> +identifier fn, _errp;
> +position p1, p2;
> +@@
> +
> + fn(..., Error **_errp, ...)
> + {
> +     ...
> +(
> +     error_propagate_prepend(_errp, ...);@p1
> +|
> +     error_propagate(_errp, ...);@p1
> +)
> +     ...
> +(
> +     error_propagate_prepend(_errp, ...);@p2
> +|
> +     error_propagate(_errp, ...);@p2
> +)
> +     ... when any
> + }
> +
> +@ script:python @
> +fn << check2.fn;
> +p1 << check2.p1;
> +p2 << check2.p2;
> +@@
> +
> +print('Warning: function {} propagates to errp several times in '
> +      'one control flow: at {}:{} and then at {}:{}'.format(
> +          fn, p1[0].file, p1[0].line, p2[0].file, p2[0].line))
> +
> +// Match functions with propagation of local error to errp.
> +// We want to refer these functions in several following rules, but I
> +// don't know a proper way to inherit a function, not just its name
> +// (to not match another functions with same name in following rules).
> +// Not-proper way is as follows: rename errp parameter in functions
> +// header and match it in following rules. Rename it back after all
> +// transformations.
> +//
> +// The common case is a single definition of local_err with at most one
> +// error_propagate_prepend() or error_propagate() on each control-flow
> +// path. Functions with multiple definitions or propagates we want to
> +// examine manually. Later rules emit warnings to guide us to them.

"Later rules" is no longer correct.  Suggest "Rules check1 and check2".

> +//
> +// Note that we match not only this "common case", but any function,
> +// which has the "common cose" on at least one control-flow path.

I appreciate this note.

Typo: s/cose/case/

> +@rule1 disable optional_qualifier exists@
> +identifier fn, local_err;
> +symbol errp;
> +@@
> +
> + fn(..., Error **
> +-    errp
> ++    ____
> +    , ...)
> + {
> +     ...
> +     Error *local_err = NULL;
> +     ...
> +(
> +     error_propagate_prepend(errp, local_err, ...);
> +|
> +     error_propagate(errp, local_err);
> +)
> +     ...
> + }
> +
> +// Convert special case with goto separately.
> +// I tried merging this into the following rule the obvious way, but
> +// it made Coccinelle hang on block.c
> +//
> +// Note interesting thing: if we don't do it here, and try to fixup
> +// "out: }" things later after all transformations (the rule will be
> +// the same, just without error_propagate() call), coccinelle fails to
> +// match this "out: }".
> +@ disable optional_qualifier@
> +identifier rule1.fn, rule1.local_err, out;
> +symbol errp;
> +@@
> +
> + fn(..., Error ** ____, ...)
> + {
> +     <...
> +-    goto out;
> ++    return;
> +     ...>
> +- out:
> +-    error_propagate(errp, local_err);
> + }
> +
> +// Convert most of local_err related stuff.
> +//
> +// Note, that we inherit rule1.fn and rule1.local_err names, not
> +// objects themselves. We may match something not related to the
> +// pattern matched by rule1. For example, local_err may be defined with
> +// the same name in different blocks inside one function, and in one
> +// block follow the propagation pattern and in other block doesn't.
> +//
> +// Note also that errp-cleaning functions
> +//   error_free_errp
> +//   error_report_errp
> +//   error_reportf_errp
> +//   warn_report_errp
> +//   warn_reportf_errp
> +// are not yet implemented. They must call corresponding Error* -
> +// freeing function and then set *errp to NULL, to avoid further
> +// propagation to original errp (consider ERRP_AUTO_PROPAGATE in use).
> +// For example, error_free_errp may look like this:
> +//
> +//    void error_free_errp(Error **errp)
> +//    {
> +//        error_free(*errp);
> +//        *errp = NULL;
> +//    }
> +@ disable optional_qualifier exists@
> +identifier rule1.fn, rule1.local_err;
> +expression list args;
> +symbol errp;
> +@@
> +
> + fn(..., Error ** ____, ...)
> + {
> +     <...
> +(
> +-    Error *local_err = NULL;
> +|
> +
> +// Convert error clearing functions
> +(
> +-    error_free(local_err);
> ++    error_free_errp(errp);
> +|
> +-    error_report_err(local_err);
> ++    error_report_errp(errp);
> +|
> +-    error_reportf_err(local_err, args);
> ++    error_reportf_errp(errp, args);
> +|
> +-    warn_report_err(local_err);
> ++    warn_report_errp(errp);
> +|
> +-    warn_reportf_err(local_err, args);
> ++    warn_reportf_errp(errp, args);
> +)
> +?-    local_err = NULL;
> +
> +|
> +-    error_propagate_prepend(errp, local_err, args);
> ++    error_prepend(errp, args);
> +|
> +-    error_propagate(errp, local_err);
> +|
> +-    &local_err
> ++    errp
> +)
> +     ...>
> + }
> +
> +// Convert remaining local_err usage. For example, different kinds of
> +// error checking in if conditionals. We can't merge this into
> +// previous hunk, as this conflicts with other substitutions in it (at
> +// least with "- local_err = NULL").
> +@ disable optional_qualifier@
> +identifier rule1.fn, rule1.local_err;
> +symbol errp;
> +@@
> +
> + fn(..., Error ** ____, ...)
> + {
> +     <...
> +-    local_err
> ++    *errp
> +     ...>
> + }
> +
> +// Always use the same pattern for checking error
> +@ disable optional_qualifier@
> +identifier rule1.fn;
> +symbol errp;
> +@@
> +
> + fn(..., Error ** ____, ...)
> + {
> +     <...
> +-    *errp != NULL
> ++    *errp
> +     ...>
> + }
> +
> +// Revert temporary ___ identifier.
> +@ disable optional_qualifier@
> +identifier rule1.fn;
> +@@
> +
> + fn(..., Error **
> +-   ____
> ++   errp
> +    , ...)
> + {
> +     ...
> + }
> diff --git a/include/qapi/error.h b/include/qapi/error.h
> index 30140d9bfe..56c133520d 100644
> --- a/include/qapi/error.h
> +++ b/include/qapi/error.h
> @@ -214,6 +214,9 @@
>   *         }
>   *         ...
>   *     }
> + *
> + * For mass-conversion use script
> + *   scripts/coccinelle/auto-propagated-errp.cocci
>   */
>  
>  #ifndef ERROR_H
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 32867bc636..8b77127c35 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2016,6 +2016,7 @@ F: include/qemu/error-report.h
>  F: qapi/error.json
>  F: util/error.c
>  F: util/qemu-error.c
> +F: scripts/coccinelle/*err*.cocci
>  
>  GDB stub
>  M: Alex Bennée <alex.bennee@linaro.org>

With the minor comment issues addressed:
Reviewed-by: Markus Armbruster <armbru@redhat.com>


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[Xen-devel] [PATCH v10 9/9] xen: introduce ERRP_AUTO_PROPAGATE

[Vladimir Sementsov-Ogievskiy]

If we want to add some info to errp (by error_prepend() or
error_append_hint()), we must use the ERRP_AUTO_PROPAGATE macro.
Otherwise, this info will not be added when errp == &error_fatal
(the program will exit prior to the error_append_hint() or
error_prepend() call).  Fix such cases.

If we want to check error after errp-function call, we need to
introduce local_err and then propagate it to errp. Instead, use
ERRP_AUTO_PROPAGATE macro, benefits are:
1. No need of explicit error_propagate call
2. No need of explicit local_err variable: use errp directly
3. ERRP_AUTO_PROPAGATE leaves errp as is if it's not NULL or
   &error_fatal, this means that we don't break error_abort
   (we'll abort on error_set, not on error_propagate)

This commit is generated by command

    sed -n '/^X86 Xen CPUs$/,/^$/{s/^F: //p}' MAINTAINERS | \
    xargs git ls-files | grep '\.[hc]$' | \
    xargs spatch \
        --sp-file scripts/coccinelle/auto-propagated-errp.cocci \
        --macro-file scripts/cocci-macro-file.h \
        --in-place --no-show-diff --max-width 80

Reported-by: Kevin Wolf <kwolf@redhat.com>
Reported-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Paul Durrant <paul@xen.org>
---
 hw/block/dataplane/xen-block.c |  17 ++---
 hw/block/xen-block.c           | 122 ++++++++++++++-------------------
 hw/pci-host/xen_igd_pt.c       |   7 +-
 hw/xen/xen-backend.c           |   7 +-
 hw/xen/xen-bus.c               |  92 +++++++++++--------------
 hw/xen/xen-host-pci-device.c   |  27 ++++----
 hw/xen/xen_pt.c                |  25 +++----
 hw/xen/xen_pt_config_init.c    |  20 +++---
 8 files changed, 138 insertions(+), 179 deletions(-)

diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c
index 288a87a814..3a8469fe87 100644
--- a/hw/block/dataplane/xen-block.c
+++ b/hw/block/dataplane/xen-block.c
@@ -739,8 +739,8 @@ void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
                                unsigned int protocol,
                                Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenDevice *xendev = dataplane->xendev;
-    Error *local_err = NULL;
     unsigned int ring_size;
     unsigned int i;
 
@@ -776,9 +776,8 @@ void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
     }
 
     xen_device_set_max_grant_refs(xendev, dataplane->nr_ring_ref,
-                                  &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
+                                  errp);
+    if (*errp) {
         goto stop;
     }
 
@@ -786,9 +785,8 @@ void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
                                               dataplane->ring_ref,
                                               dataplane->nr_ring_ref,
                                               PROT_READ | PROT_WRITE,
-                                              &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
+                                              errp);
+    if (*errp) {
         goto stop;
     }
 
@@ -821,9 +819,8 @@ void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
     dataplane->event_channel =
         xen_device_bind_event_channel(xendev, event_channel,
                                       xen_block_dataplane_event, dataplane,
-                                      &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
+                                      errp);
+    if (*errp) {
         goto stop;
     }
 
diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index 7b3b6dee97..5d4c94181c 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -195,6 +195,7 @@ static const BlockDevOps xen_block_dev_ops = {
 
 static void xen_block_realize(XenDevice *xendev, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenBlockDevice *blockdev = XEN_BLOCK_DEVICE(xendev);
     XenBlockDeviceClass *blockdev_class =
         XEN_BLOCK_DEVICE_GET_CLASS(xendev);
@@ -202,7 +203,6 @@ static void xen_block_realize(XenDevice *xendev, Error **errp)
     XenBlockVdev *vdev = &blockdev->props.vdev;
     BlockConf *conf = &blockdev->props.conf;
     BlockBackend *blk = conf->blk;
-    Error *local_err = NULL;
 
     if (vdev->type == XEN_BLOCK_VDEV_TYPE_INVALID) {
         error_setg(errp, "vdev property not set");
@@ -212,9 +212,8 @@ static void xen_block_realize(XenDevice *xendev, Error **errp)
     trace_xen_block_realize(type, vdev->disk, vdev->partition);
 
     if (blockdev_class->realize) {
-        blockdev_class->realize(blockdev, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        blockdev_class->realize(blockdev, errp);
+        if (*errp) {
             return;
         }
     }
@@ -284,8 +283,8 @@ static void xen_block_frontend_changed(XenDevice *xendev,
                                        enum xenbus_state frontend_state,
                                        Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     enum xenbus_state backend_state = xen_device_backend_get_state(xendev);
-    Error *local_err = NULL;
 
     switch (frontend_state) {
     case XenbusStateInitialised:
@@ -294,15 +293,13 @@ static void xen_block_frontend_changed(XenDevice *xendev,
             break;
         }
 
-        xen_block_disconnect(xendev, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        xen_block_disconnect(xendev, errp);
+        if (*errp) {
             break;
         }
 
-        xen_block_connect(xendev, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        xen_block_connect(xendev, errp);
+        if (*errp) {
             break;
         }
 
@@ -315,9 +312,8 @@ static void xen_block_frontend_changed(XenDevice *xendev,
 
     case XenbusStateClosed:
     case XenbusStateUnknown:
-        xen_block_disconnect(xendev, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        xen_block_disconnect(xendev, errp);
+        if (*errp) {
             break;
         }
 
@@ -404,10 +400,10 @@ static int vbd_name_to_disk(const char *name, const char **endp,
 static void xen_block_set_vdev(Object *obj, Visitor *v, const char *name,
                                void *opaque, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     DeviceState *dev = DEVICE(obj);
     Property *prop = opaque;
     XenBlockVdev *vdev = qdev_get_prop_ptr(dev, prop);
-    Error *local_err = NULL;
     char *str, *p;
     const char *end;
 
@@ -416,9 +412,8 @@ static void xen_block_set_vdev(Object *obj, Visitor *v, const char *name,
         return;
     }
 
-    visit_type_str(v, name, &str, &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
+    visit_type_str(v, name, &str, errp);
+    if (*errp) {
         return;
     }
 
@@ -672,9 +667,9 @@ static void xen_block_blockdev_del(const char *node_name, Error **errp)
 static char *xen_block_blockdev_add(const char *id, QDict *qdict,
                                     Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     const char *driver = qdict_get_try_str(qdict, "driver");
     BlockdevOptions *options = NULL;
-    Error *local_err = NULL;
     char *node_name;
     Visitor *v;
 
@@ -689,18 +684,16 @@ static char *xen_block_blockdev_add(const char *id, QDict *qdict,
     trace_xen_block_blockdev_add(node_name);
 
     v = qobject_input_visitor_new(QOBJECT(qdict));
-    visit_type_BlockdevOptions(v, NULL, &options, &local_err);
+    visit_type_BlockdevOptions(v, NULL, &options, errp);
     visit_free(v);
 
-    if (local_err) {
-        error_propagate(errp, local_err);
+    if (*errp) {
         goto fail;
     }
 
-    qmp_blockdev_add(options, &local_err);
+    qmp_blockdev_add(options, errp);
 
-    if (local_err) {
-        error_propagate(errp, local_err);
+    if (*errp) {
         goto fail;
     }
 
@@ -719,14 +712,12 @@ fail:
 
 static void xen_block_drive_destroy(XenBlockDrive *drive, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     char *node_name = drive->node_name;
 
     if (node_name) {
-        Error *local_err = NULL;
-
-        xen_block_blockdev_del(node_name, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        xen_block_blockdev_del(node_name, errp);
+        if (*errp) {
             return;
         }
         g_free(node_name);
@@ -740,6 +731,7 @@ static XenBlockDrive *xen_block_drive_create(const char *id,
                                              const char *device_type,
                                              QDict *opts, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     const char *params = qdict_get_try_str(opts, "params");
     const char *mode = qdict_get_try_str(opts, "mode");
     const char *direct_io_safe = qdict_get_try_str(opts, "direct-io-safe");
@@ -747,7 +739,6 @@ static XenBlockDrive *xen_block_drive_create(const char *id,
     char *driver = NULL;
     char *filename = NULL;
     XenBlockDrive *drive = NULL;
-    Error *local_err = NULL;
     QDict *file_layer;
     QDict *driver_layer;
 
@@ -826,13 +817,12 @@ static XenBlockDrive *xen_block_drive_create(const char *id,
 
     g_assert(!drive->node_name);
     drive->node_name = xen_block_blockdev_add(drive->id, driver_layer,
-                                              &local_err);
+                                              errp);
 
     qobject_unref(driver_layer);
 
 done:
-    if (local_err) {
-        error_propagate(errp, local_err);
+    if (*errp) {
         xen_block_drive_destroy(drive, NULL);
         return NULL;
     }
@@ -857,8 +847,8 @@ static void xen_block_iothread_destroy(XenBlockIOThread *iothread,
 static XenBlockIOThread *xen_block_iothread_create(const char *id,
                                                    Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenBlockIOThread *iothread = g_new(XenBlockIOThread, 1);
-    Error *local_err = NULL;
     QDict *opts;
     QObject *ret_data;
 
@@ -867,13 +857,11 @@ static XenBlockIOThread *xen_block_iothread_create(const char *id,
     opts = qdict_new();
     qdict_put_str(opts, "qom-type", TYPE_IOTHREAD);
     qdict_put_str(opts, "id", id);
-    qmp_object_add(opts, &ret_data, &local_err);
+    qmp_object_add(opts, &ret_data, errp);
     qobject_unref(opts);
     qobject_unref(ret_data);
 
-    if (local_err) {
-        error_propagate(errp, local_err);
-
+    if (*errp) {
         g_free(iothread->id);
         g_free(iothread);
         return NULL;
@@ -885,6 +873,7 @@ static XenBlockIOThread *xen_block_iothread_create(const char *id,
 static void xen_block_device_create(XenBackendInstance *backend,
                                     QDict *opts, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenBus *xenbus = xen_backend_get_bus(backend);
     const char *name = xen_backend_get_name(backend);
     unsigned long number;
@@ -892,7 +881,6 @@ static void xen_block_device_create(XenBackendInstance *backend,
     XenBlockDrive *drive = NULL;
     XenBlockIOThread *iothread = NULL;
     XenDevice *xendev = NULL;
-    Error *local_err = NULL;
     const char *type;
     XenBlockDevice *blockdev;
 
@@ -924,52 +912,48 @@ static void xen_block_device_create(XenBackendInstance *backend,
         goto fail;
     }
 
-    drive = xen_block_drive_create(vdev, device_type, opts, &local_err);
+    drive = xen_block_drive_create(vdev, device_type, opts, errp);
     if (!drive) {
-        error_propagate_prepend(errp, local_err, "failed to create drive: ");
+        error_prepend(errp, "failed to create drive: ");
         goto fail;
     }
 
-    iothread = xen_block_iothread_create(vdev, &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to create iothread: ");
+    iothread = xen_block_iothread_create(vdev, errp);
+    if (*errp) {
+        error_prepend(errp, "failed to create iothread: ");
         goto fail;
     }
 
     xendev = XEN_DEVICE(qdev_create(BUS(xenbus), type));
     blockdev = XEN_BLOCK_DEVICE(xendev);
 
-    object_property_set_str(OBJECT(xendev), vdev, "vdev", &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err, "failed to set 'vdev': ");
+    object_property_set_str(OBJECT(xendev), vdev, "vdev", errp);
+    if (*errp) {
+        error_prepend(errp, "failed to set 'vdev': ");
         goto fail;
     }
 
     object_property_set_str(OBJECT(xendev),
                             xen_block_drive_get_node_name(drive), "drive",
-                            &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err, "failed to set 'drive': ");
+                            errp);
+    if (*errp) {
+        error_prepend(errp, "failed to set 'drive': ");
         goto fail;
     }
 
     object_property_set_str(OBJECT(xendev), iothread->id, "iothread",
-                            &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to set 'iothread': ");
+                            errp);
+    if (*errp) {
+        error_prepend(errp, "failed to set 'iothread': ");
         goto fail;
     }
 
     blockdev->iothread = iothread;
     blockdev->drive = drive;
 
-    object_property_set_bool(OBJECT(xendev), true, "realized", &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "realization of device %s failed: ",
-                                type);
+    object_property_set_bool(OBJECT(xendev), true, "realized", errp);
+    if (*errp) {
+        error_prepend(errp, "realization of device %s failed: ", type);
         goto fail;
     }
 
@@ -993,31 +977,29 @@ fail:
 static void xen_block_device_destroy(XenBackendInstance *backend,
                                      Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenDevice *xendev = xen_backend_get_device(backend);
     XenBlockDevice *blockdev = XEN_BLOCK_DEVICE(xendev);
     XenBlockVdev *vdev = &blockdev->props.vdev;
     XenBlockDrive *drive = blockdev->drive;
     XenBlockIOThread *iothread = blockdev->iothread;
-    Error *local_err = NULL;
 
     trace_xen_block_device_destroy(vdev->number);
 
     object_unparent(OBJECT(xendev));
 
     if (iothread) {
-        xen_block_iothread_destroy(iothread, &local_err);
-        if (local_err) {
-            error_propagate_prepend(errp, local_err,
-                                "failed to destroy iothread: ");
+        xen_block_iothread_destroy(iothread, errp);
+        if (*errp) {
+            error_prepend(errp, "failed to destroy iothread: ");
             return;
         }
     }
 
     if (drive) {
-        xen_block_drive_destroy(drive, &local_err);
-        if (local_err) {
-            error_propagate_prepend(errp, local_err,
-                                "failed to destroy drive: ");
+        xen_block_drive_destroy(drive, errp);
+        if (*errp) {
+            error_prepend(errp, "failed to destroy drive: ");
         }
     }
 }
diff --git a/hw/pci-host/xen_igd_pt.c b/hw/pci-host/xen_igd_pt.c
index efcc9347ff..29ade9ca25 100644
--- a/hw/pci-host/xen_igd_pt.c
+++ b/hw/pci-host/xen_igd_pt.c
@@ -79,17 +79,16 @@ static void host_pci_config_read(int pos, int len, uint32_t *val, Error **errp)
 
 static void igd_pt_i440fx_realize(PCIDevice *pci_dev, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     uint32_t val = 0;
     size_t i;
     int pos, len;
-    Error *local_err = NULL;
 
     for (i = 0; i < ARRAY_SIZE(igd_host_bridge_infos); i++) {
         pos = igd_host_bridge_infos[i].offset;
         len = igd_host_bridge_infos[i].len;
-        host_pci_config_read(pos, len, &val, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        host_pci_config_read(pos, len, &val, errp);
+        if (*errp) {
             return;
         }
         pci_default_write_config(pci_dev, pos, val, len);
diff --git a/hw/xen/xen-backend.c b/hw/xen/xen-backend.c
index da065f81b7..1cc0694053 100644
--- a/hw/xen/xen-backend.c
+++ b/hw/xen/xen-backend.c
@@ -98,9 +98,9 @@ static void xen_backend_list_remove(XenBackendInstance *backend)
 void xen_backend_device_create(XenBus *xenbus, const char *type,
                                const char *name, QDict *opts, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     const XenBackendImpl *impl = xen_backend_table_lookup(type);
     XenBackendInstance *backend;
-    Error *local_error = NULL;
 
     if (!impl) {
         return;
@@ -110,9 +110,8 @@ void xen_backend_device_create(XenBus *xenbus, const char *type,
     backend->xenbus = xenbus;
     backend->name = g_strdup(name);
 
-    impl->create(backend, opts, &local_error);
-    if (local_error) {
-        error_propagate(errp, local_error);
+    impl->create(backend, opts, errp);
+    if (*errp) {
         g_free(backend->name);
         g_free(backend);
         return;
diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 18237b34ea..97259c964b 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -53,9 +53,9 @@ static char *xen_device_get_frontend_path(XenDevice *xendev)
 
 static void xen_device_unplug(XenDevice *xendev, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
     const char *type = object_get_typename(OBJECT(xendev));
-    Error *local_err = NULL;
     xs_transaction_t tid;
 
     trace_xen_device_unplug(type, xendev->name);
@@ -69,14 +69,14 @@ again:
     }
 
     xs_node_printf(xenbus->xsh, tid, xendev->backend_path, "online",
-                   &local_err, "%u", 0);
-    if (local_err) {
+                   errp, "%u", 0);
+    if (*errp) {
         goto abort;
     }
 
     xs_node_printf(xenbus->xsh, tid, xendev->backend_path, "state",
-                   &local_err, "%u", XenbusStateClosing);
-    if (local_err) {
+                   errp, "%u", XenbusStateClosing);
+    if (*errp) {
         goto abort;
     }
 
@@ -96,7 +96,6 @@ abort:
      * from ending the transaction.
      */
     xs_transaction_end(xenbus->xsh, tid, true);
-    error_propagate(errp, local_err);
 }
 
 static void xen_bus_print_dev(Monitor *mon, DeviceState *dev, int indent)
@@ -205,15 +204,13 @@ static XenWatch *watch_list_add(XenWatchList *watch_list, const char *node,
                                 const char *key, XenWatchHandler handler,
                                 void *opaque, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenWatch *watch = new_watch(node, key, handler, opaque);
-    Error *local_err = NULL;
 
     notifier_list_add(&watch_list->notifiers, &watch->notifier);
 
-    xs_node_watch(watch_list->xsh, node, key, watch->token, &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
-
+    xs_node_watch(watch_list->xsh, node, key, watch->token, errp);
+    if (*errp) {
         notifier_remove(&watch->notifier);
         free_watch(watch);
 
@@ -255,11 +252,11 @@ static void xen_bus_backend_create(XenBus *xenbus, const char *type,
                                    const char *name, char *path,
                                    Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     xs_transaction_t tid;
     char **key;
     QDict *opts;
     unsigned int i, n;
-    Error *local_err = NULL;
 
     trace_xen_bus_backend_create(type, path);
 
@@ -314,13 +311,11 @@ again:
         return;
     }
 
-    xen_backend_device_create(xenbus, type, name, opts, &local_err);
+    xen_backend_device_create(xenbus, type, name, opts, errp);
     qobject_unref(opts);
 
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to create '%s' device '%s': ",
-                                type, name);
+    if (*errp) {
+        error_prepend(errp, "failed to create '%s' device '%s': ", type, name);
     }
 }
 
@@ -692,9 +687,9 @@ static void xen_device_remove_watch(XenDevice *xendev, XenWatch *watch,
 
 static void xen_device_backend_create(XenDevice *xendev, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
     struct xs_permissions perms[2];
-    Error *local_err = NULL;
 
     xendev->backend_path = xen_device_get_backend_path(xendev);
 
@@ -706,30 +701,27 @@ static void xen_device_backend_create(XenDevice *xendev, Error **errp)
     g_assert(xenbus->xsh);
 
     xs_node_create(xenbus->xsh, XBT_NULL, xendev->backend_path, perms,
-                   ARRAY_SIZE(perms), &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to create backend: ");
+                   ARRAY_SIZE(perms), errp);
+    if (*errp) {
+        error_prepend(errp, "failed to create backend: ");
         return;
     }
 
     xendev->backend_state_watch =
         xen_device_add_watch(xendev, xendev->backend_path,
                              "state", xen_device_backend_changed,
-                             &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to watch backend state: ");
+                             errp);
+    if (*errp) {
+        error_prepend(errp, "failed to watch backend state: ");
         return;
     }
 
     xendev->backend_online_watch =
         xen_device_add_watch(xendev, xendev->backend_path,
                              "online", xen_device_backend_changed,
-                             &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to watch backend online: ");
+                             errp);
+    if (*errp) {
+        error_prepend(errp, "failed to watch backend online: ");
         return;
     }
 }
@@ -866,9 +858,9 @@ static bool xen_device_frontend_exists(XenDevice *xendev)
 
 static void xen_device_frontend_create(XenDevice *xendev, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
     struct xs_permissions perms[2];
-    Error *local_err = NULL;
 
     xendev->frontend_path = xen_device_get_frontend_path(xendev);
 
@@ -885,20 +877,18 @@ static void xen_device_frontend_create(XenDevice *xendev, Error **errp)
         g_assert(xenbus->xsh);
 
         xs_node_create(xenbus->xsh, XBT_NULL, xendev->frontend_path, perms,
-                       ARRAY_SIZE(perms), &local_err);
-        if (local_err) {
-            error_propagate_prepend(errp, local_err,
-                                    "failed to create frontend: ");
+                       ARRAY_SIZE(perms), errp);
+        if (*errp) {
+            error_prepend(errp, "failed to create frontend: ");
             return;
         }
     }
 
     xendev->frontend_state_watch =
         xen_device_add_watch(xendev, xendev->frontend_path, "state",
-                             xen_device_frontend_changed, &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to watch frontend state: ");
+                             xen_device_frontend_changed, errp);
+    if (*errp) {
+        error_prepend(errp, "failed to watch frontend state: ");
     }
 }
 
@@ -1247,11 +1237,11 @@ static void xen_device_exit(Notifier *n, void *data)
 
 static void xen_device_realize(DeviceState *dev, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenDevice *xendev = XEN_DEVICE(dev);
     XenDeviceClass *xendev_class = XEN_DEVICE_GET_CLASS(xendev);
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
     const char *type = object_get_typename(OBJECT(xendev));
-    Error *local_err = NULL;
 
     if (xendev->frontend_id == DOMID_INVALID) {
         xendev->frontend_id = xen_domid;
@@ -1267,10 +1257,9 @@ static void xen_device_realize(DeviceState *dev, Error **errp)
         goto unrealize;
     }
 
-    xendev->name = xendev_class->get_name(xendev, &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to get device name: ");
+    xendev->name = xendev_class->get_name(xendev, errp);
+    if (*errp) {
+        error_prepend(errp, "failed to get device name: ");
         goto unrealize;
     }
 
@@ -1293,22 +1282,19 @@ static void xen_device_realize(DeviceState *dev, Error **errp)
     xendev->feature_grant_copy =
         (xengnttab_grant_copy(xendev->xgth, 0, NULL) == 0);
 
-    xen_device_backend_create(xendev, &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
+    xen_device_backend_create(xendev, errp);
+    if (*errp) {
         goto unrealize;
     }
 
-    xen_device_frontend_create(xendev, &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
+    xen_device_frontend_create(xendev, errp);
+    if (*errp) {
         goto unrealize;
     }
 
     if (xendev_class->realize) {
-        xendev_class->realize(xendev, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        xendev_class->realize(xendev, errp);
+        if (*errp) {
             goto unrealize;
         }
     }
diff --git a/hw/xen/xen-host-pci-device.c b/hw/xen/xen-host-pci-device.c
index 1b44dcafaf..02379c341c 100644
--- a/hw/xen/xen-host-pci-device.c
+++ b/hw/xen/xen-host-pci-device.c
@@ -333,8 +333,8 @@ void xen_host_pci_device_get(XenHostPCIDevice *d, uint16_t domain,
                              uint8_t bus, uint8_t dev, uint8_t func,
                              Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     unsigned int v;
-    Error *err = NULL;
 
     d->config_fd = -1;
     d->domain = domain;
@@ -342,36 +342,36 @@ void xen_host_pci_device_get(XenHostPCIDevice *d, uint16_t domain,
     d->dev = dev;
     d->func = func;
 
-    xen_host_pci_config_open(d, &err);
-    if (err) {
+    xen_host_pci_config_open(d, errp);
+    if (*errp) {
         goto error;
     }
 
-    xen_host_pci_get_resource(d, &err);
-    if (err) {
+    xen_host_pci_get_resource(d, errp);
+    if (*errp) {
         goto error;
     }
 
-    xen_host_pci_get_hex_value(d, "vendor", &v, &err);
-    if (err) {
+    xen_host_pci_get_hex_value(d, "vendor", &v, errp);
+    if (*errp) {
         goto error;
     }
     d->vendor_id = v;
 
-    xen_host_pci_get_hex_value(d, "device", &v, &err);
-    if (err) {
+    xen_host_pci_get_hex_value(d, "device", &v, errp);
+    if (*errp) {
         goto error;
     }
     d->device_id = v;
 
-    xen_host_pci_get_dec_value(d, "irq", &v, &err);
-    if (err) {
+    xen_host_pci_get_dec_value(d, "irq", &v, errp);
+    if (*errp) {
         goto error;
     }
     d->irq = v;
 
-    xen_host_pci_get_hex_value(d, "class", &v, &err);
-    if (err) {
+    xen_host_pci_get_hex_value(d, "class", &v, errp);
+    if (*errp) {
         goto error;
     }
     d->class_code = v;
@@ -381,7 +381,6 @@ void xen_host_pci_device_get(XenHostPCIDevice *d, uint16_t domain,
     return;
 
 error:
-    error_propagate(errp, err);
 
     if (d->config_fd >= 0) {
         close(d->config_fd);
diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
index b91082cb8b..f57b81588e 100644
--- a/hw/xen/xen_pt.c
+++ b/hw/xen/xen_pt.c
@@ -767,12 +767,12 @@ static void xen_pt_destroy(PCIDevice *d) {
 
 static void xen_pt_realize(PCIDevice *d, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     XenPCIPassthroughState *s = XEN_PT_DEVICE(d);
     int i, rc = 0;
     uint8_t machine_irq = 0, scratch;
     uint16_t cmd = 0;
     int pirq = XEN_PT_UNASSIGNED_PIRQ;
-    Error *err = NULL;
 
     /* register real device */
     XEN_PT_LOG(d, "Assigning real physical device %02x:%02x.%d"
@@ -783,10 +783,9 @@ static void xen_pt_realize(PCIDevice *d, Error **errp)
     xen_host_pci_device_get(&s->real_device,
                             s->hostaddr.domain, s->hostaddr.bus,
                             s->hostaddr.slot, s->hostaddr.function,
-                            &err);
-    if (err) {
-        error_append_hint(&err, "Failed to \"open\" the real pci device");
-        error_propagate(errp, err);
+                            errp);
+    if (*errp) {
+        error_append_hint(errp, "Failed to \"open\" the real pci device");
         return;
     }
 
@@ -813,11 +812,10 @@ static void xen_pt_realize(PCIDevice *d, Error **errp)
             return;
         }
 
-        xen_pt_setup_vga(s, &s->real_device, &err);
-        if (err) {
-            error_append_hint(&err, "Setup VGA BIOS of passthrough"
-                    " GFX failed");
-            error_propagate(errp, err);
+        xen_pt_setup_vga(s, &s->real_device, errp);
+        if (*errp) {
+            error_append_hint(errp, "Setup VGA BIOS of passthrough"
+                              " GFX failed");
             xen_host_pci_device_put(&s->real_device);
             return;
         }
@@ -830,10 +828,9 @@ static void xen_pt_realize(PCIDevice *d, Error **errp)
     xen_pt_register_regions(s, &cmd);
 
     /* reinitialize each config register to be emulated */
-    xen_pt_config_init(s, &err);
-    if (err) {
-        error_append_hint(&err, "PCI Config space initialisation failed");
-        error_propagate(errp, err);
+    xen_pt_config_init(s, errp);
+    if (*errp) {
+        error_append_hint(errp, "PCI Config space initialisation failed");
         rc = -1;
         goto err_out;
     }
diff --git a/hw/xen/xen_pt_config_init.c b/hw/xen/xen_pt_config_init.c
index 31ec5add1d..af3fbd1bfb 100644
--- a/hw/xen/xen_pt_config_init.c
+++ b/hw/xen/xen_pt_config_init.c
@@ -2008,8 +2008,8 @@ static void xen_pt_config_reg_init(XenPCIPassthroughState *s,
 
 void xen_pt_config_init(XenPCIPassthroughState *s, Error **errp)
 {
+    ERRP_AUTO_PROPAGATE();
     int i, rc;
-    Error *err = NULL;
 
     QLIST_INIT(&s->reg_grps);
 
@@ -2052,10 +2052,9 @@ void xen_pt_config_init(XenPCIPassthroughState *s, Error **errp)
                                                   reg_grp_offset,
                                                   &reg_grp_entry->size);
             if (rc < 0) {
-                error_setg(&err, "Failed to initialize %d/%zu, type = 0x%x,"
+                error_setg(errp, "Failed to initialize %d/%zu, type = 0x%x,"
                            " rc: %d", i, ARRAY_SIZE(xen_pt_emu_reg_grps),
                            xen_pt_emu_reg_grps[i].grp_type, rc);
-                error_propagate(errp, err);
                 xen_pt_config_delete(s);
                 return;
             }
@@ -2068,13 +2067,14 @@ void xen_pt_config_init(XenPCIPassthroughState *s, Error **errp)
 
                 /* initialize capability register */
                 for (j = 0; regs->size != 0; j++, regs++) {
-                    xen_pt_config_reg_init(s, reg_grp_entry, regs, &err);
-                    if (err) {
-                        error_append_hint(&err, "Failed to init register %d"
-                                " offsets 0x%x in grp_type = 0x%x (%d/%zu)", j,
-                                regs->offset, xen_pt_emu_reg_grps[i].grp_type,
-                                i, ARRAY_SIZE(xen_pt_emu_reg_grps));
-                        error_propagate(errp, err);
+                    xen_pt_config_reg_init(s, reg_grp_entry, regs, errp);
+                    if (*errp) {
+                        error_append_hint(errp, "Failed to init register %d"
+                                          " offsets 0x%x in grp_type = 0x%x (%d/%zu)",
+                                          j,
+                                          regs->offset,
+                                          xen_pt_emu_reg_grps[i].grp_type,
+                                          i, ARRAY_SIZE(xen_pt_emu_reg_grps));
                         xen_pt_config_delete(s);
                         return;
                     }
-- 
2.21.0


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