[PATCH 0/3] block: improve error reporting for unsupported O_DIRECT

[PATCH 0/3] block: improve error reporting for unsupported O_DIRECT

[Daniel P. Berrangé]

To repeat the commit message from patch 3...

Currently at startup if using cache=none on a filesystem lacking
O_DIRECT such as tmpfs, at startup QEMU prints

qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: file system may not support O_DIRECT
qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: Could not open '/tmp/foo.img': Invalid argument

while at QMP level the hint is missing, so QEMU reports just

  "error": {
      "class": "GenericError",
      "desc": "Could not open '/tmp/foo.img': Invalid argument"
  }

which is close to useless for the end user trying to figure out what
they did wrong

With this change at startup QEMU prints

qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: Unable to open '/tmp/foo.img' flags 0x4000: filesystem does not support O_DIRECT

while at the QMP level QEMU reports a massively more informative

  "error": {
     "class": "GenericError",
     "desc": "Unable to open '/tmp/foo.img' flags 0x4002: filesystem does not support O_DIRECT"
  }


qemu_open is used in many more places besides block layer, but
converting those to qemu_open_err is left as an exercise for
other maintainers.

Daniel P. Berrangé (3):
  util: validate whether O_DIRECT is supported after failure
  util: support detailed error reporting for qemu_open
  block: switch to use qemu_open_err for improved errors

 block/file-posix.c   | 10 +++----
 include/qemu/osdep.h |  1 +
 util/osdep.c         | 70 ++++++++++++++++++++++++++++++++++++++------
 3 files changed, 66 insertions(+), 15 deletions(-)

-- 
2.26.2

[PATCH 1/3] util: validate whether O_DIRECT is supported after failure

[Daniel P. Berrangé]

Currently we suggest that a filesystem may not support O_DIRECT after
seeing an EINVAL. Other things can cause EINVAL though, so it is better
to do an explicit check, and then report a definitive error message.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 util/osdep.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/util/osdep.c b/util/osdep.c
index 4829c07ff6..4bdbe81cec 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -342,8 +342,17 @@ int qemu_open(const char *name, int flags, ...)
 
 #ifdef O_DIRECT
     if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
-        error_report("file system may not support O_DIRECT");
-        errno = EINVAL; /* in case it was clobbered */
+        int newflags = flags & ~O_DIRECT;
+# ifdef O_CLOEXEC
+        ret = open(name, newflags | O_CLOEXEC, mode);
+# else
+        ret = open(name, newflags, mode);
+# endif
+        if (ret != -1) {
+            close(ret);
+            error_report("file system does not support O_DIRECT");
+            errno = EINVAL;
+        }
     }
 #endif /* O_DIRECT */
 
-- 
2.26.2

[PATCH 2/3] util: support detailed error reporting for qemu_open

[Daniel P. Berrangé]

Create a "qemu_open_err" method which does the same as "qemu_open",
but with a "Error **errp" for error reporting. There should be no
behavioural difference for existing callers at this stage.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/qemu/osdep.h |  1 +
 util/osdep.c         | 71 +++++++++++++++++++++++++++++++++++---------
 2 files changed, 58 insertions(+), 14 deletions(-)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 0d26a1b9bd..e41701a308 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -483,6 +483,7 @@ int qemu_madvise(void *addr, size_t len, int advice);
 int qemu_mprotect_rwx(void *addr, size_t size);
 int qemu_mprotect_none(void *addr, size_t size);
 
+int qemu_open_err(const char *name, int flags, Error **errp, ...);
 int qemu_open(const char *name, int flags, ...);
 int qemu_close(int fd);
 int qemu_unlink(const char *name);
diff --git a/util/osdep.c b/util/osdep.c
index 4bdbe81cec..450b3a5da3 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -22,6 +22,7 @@
  * THE SOFTWARE.
  */
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 
 /* Needed early for CONFIG_BSD etc. */
 
@@ -282,7 +283,7 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
 /*
  * Opens a file with FD_CLOEXEC set
  */
-int qemu_open(const char *name, int flags, ...)
+static int qemu_openv(const char *name, int flags, Error **errp, va_list ap)
 {
     int ret;
     int mode = 0;
@@ -297,24 +298,31 @@ int qemu_open(const char *name, int flags, ...)
 
         fdset_id = qemu_parse_fdset(fdset_id_str);
         if (fdset_id == -1) {
+            error_setg(errp, "Unable to parse fdset %s", name);
             errno = EINVAL;
             return -1;
         }
 
         fd = monitor_fdset_get_fd(fdset_id, flags);
         if (fd < 0) {
+            error_setg_errno(errp, -fd, "Unable acquire FD for %s flags %x",
+                             name, flags);
             errno = -fd;
             return -1;
         }
 
         dupfd = qemu_dup_flags(fd, flags);
         if (dupfd == -1) {
+            error_setg_errno(errp, errno, "Unable dup FD for %s flags %x",
+                             name, flags);
             return -1;
         }
 
         ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
         if (ret == -1) {
             close(dupfd);
+            error_setg(errp, "Unable save FD for %s flags %x",
+                       name, flags);
             errno = EINVAL;
             return -1;
         }
@@ -324,11 +332,7 @@ int qemu_open(const char *name, int flags, ...)
 #endif
 
     if (flags & O_CREAT) {
-        va_list ap;
-
-        va_start(ap, flags);
         mode = va_arg(ap, int);
-        va_end(ap);
     }
 
 #ifdef O_CLOEXEC
@@ -340,25 +344,64 @@ int qemu_open(const char *name, int flags, ...)
     }
 #endif
 
+    if (ret == -1) {
+        const char *action = "open";
+        if (flags & O_CREAT) {
+            action = "create";
+        }
 #ifdef O_DIRECT
-    if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
-        int newflags = flags & ~O_DIRECT;
+        if (errno == EINVAL && (flags & O_DIRECT)) {
+            int newflags = flags & ~O_DIRECT;
 # ifdef O_CLOEXEC
-        ret = open(name, newflags | O_CLOEXEC, mode);
+            ret = open(name, newflags | O_CLOEXEC, mode);
 # else
-        ret = open(name, newflags, mode);
+            ret = open(name, newflags, mode);
 # endif
-        if (ret != -1) {
-            close(ret);
-            error_report("file system does not support O_DIRECT");
-            errno = EINVAL;
+            if (ret != -1) {
+                close(ret);
+                error_setg(errp, "Unable to %s '%s' flags 0x%x: "
+                           "filesystem does not support O_DIRECT",
+                           action, name, flags);
+                if (!errp) {
+                    error_report("file system does not support O_DIRECT");
+                }
+                errno = EINVAL;
+                return -1;
+            }
         }
-    }
 #endif /* O_DIRECT */
+        error_setg_errno(errp, errno, "Unable to %s '%s' flags 0x%x",
+                         action, name, flags);
+    }
+
 
     return ret;
 }
 
+int qemu_open_err(const char *name, int flags, Error **errp, ...)
+{
+    va_list ap;
+    int rv;
+
+    va_start(ap, errp);
+    rv = qemu_openv(name, flags, errp, ap);
+    va_end(ap);
+
+    return rv;
+}
+
+int qemu_open(const char *name, int flags, ...)
+{
+    va_list ap;
+    int rv;
+
+    va_start(ap, flags);
+    rv = qemu_openv(name, flags, NULL, ap);
+    va_end(ap);
+
+    return rv;
+}
+
 int qemu_close(int fd)
 {
     int64_t fdset_id;
-- 
2.26.2

[PATCH 3/3] block: switch to use qemu_open_err for improved errors

[Daniel P. Berrangé]

Currently at startup if using cache=none on a filesystem lacking
O_DIRECT such as tmpfs, at startup QEMU prints

qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: file system may not support O_DIRECT
qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: Could not open '/tmp/foo.img': Invalid argument

while at QMP level the hint is missing, so QEMU reports just

  "error": {
      "class": "GenericError",
      "desc": "Could not open '/tmp/foo.img': Invalid argument"
  }

which is close to useless for the end user trying to figure out what
they did wrong

With this change at startup QEMU prints

qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: Unable to open '/tmp/foo.img' flags 0x4000: filesystem does not support O_DIRECT

while at the QMP level QEMU reports a massively more informative

  "error": {
     "class": "GenericError",
     "desc": "Unable to open '/tmp/foo.img' flags 0x4002: filesystem does not support O_DIRECT"
  }

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 block/file-posix.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 3ab8f5a0fa..2865b789fb 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -574,11 +574,10 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
     raw_parse_flags(bdrv_flags, &s->open_flags, false);
 
     s->fd = -1;
-    fd = qemu_open(filename, s->open_flags, 0644);
+    fd = qemu_open_err(filename, s->open_flags, errp, 0644);
     ret = fd < 0 ? -errno : 0;
 
     if (ret < 0) {
-        error_setg_file_open(errp, -ret, filename);
         if (ret == -EROFS) {
             ret = -EACCES;
         }
@@ -970,9 +969,8 @@ static int raw_reconfigure_getfd(BlockDriverState *bs, int flags,
         ret = raw_normalize_devicepath(&normalized_filename, errp);
         if (ret >= 0) {
             assert(!(*open_flags & O_CREAT));
-            fd = qemu_open(normalized_filename, *open_flags);
+            fd = qemu_open_err(normalized_filename, *open_flags, errp);
             if (fd == -1) {
-                error_setg_errno(errp, errno, "Could not reopen file");
                 return -1;
             }
         }
@@ -2324,10 +2322,10 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
     }
 
     /* Create file */
-    fd = qemu_open(file_opts->filename, O_RDWR | O_CREAT | O_BINARY, 0644);
+    fd = qemu_open_err(file_opts->filename, O_RDWR | O_CREAT | O_BINARY,
+                       errp, 0644);
     if (fd < 0) {
         result = -errno;
-        error_setg_errno(errp, -result, "Could not create file");
         goto out;
     }
 
-- 
2.26.2

Re: [PATCH 0/3] block: improve error reporting for unsupported O_DIRECT

[no-reply]

Patchew URL: https://patchew.org/QEMU/20200701160509.1523847-1-berrange@redhat.com/



Hi,

This series failed the docker-quick@centos7 build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#!/bin/bash
make docker-image-centos7 V=1 NETWORK=1
time make docker-test-quick@centos7 SHOW_ENV=1 J=14 NETWORK=1
=== TEST SCRIPT END ===

+++ /tmp/qemu-test/build/tests/qemu-iotests/226.out.bad 2020-07-01 16:58:11.321029717 +0000
@@ -6,7 +6,7 @@
 qemu-io: can't open: A regular file was expected by the 'file' driver, but something else was given
 qemu-io: warning: Opening a character device as a file using the 'file' driver is deprecated
 == Testing RW ==
-qemu-io: can't open: Could not open 'TEST_DIR/t.IMGFMT': Is a directory
+qemu-io: can't open: Unable to open 'TEST_DIR/t.IMGFMT' flags 0x2: Is a directory
 qemu-io: warning: Opening a character device as a file using the 'file' driver is deprecated
 
 === Testing with driver:host_device ===
@@ -14,13 +14,13 @@
---
Not run: 259
Failures: 061 069 111 226 244
Failed 5 of 119 iotests
make: *** [check-tests/check-block.sh] Error 1
Traceback (most recent call last):
  File "./tests/docker/docker.py", line 669, in <module>
    sys.exit(main())
---
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '-n', 'docker', 'run', '--label', 'com.qemu.instance.uuid=67228a70e7844d70b07a864fef5c4569', '-u', '1003', '--security-opt', 'seccomp=unconfined', '--rm', '-e', 'TARGET_LIST=', '-e', 'EXTRA_CONFIGURE_OPTS=', '-e', 'V=', '-e', 'J=14', '-e', 'DEBUG=', '-e', 'SHOW_ENV=1', '-e', 'CCACHE_DIR=/var/tmp/ccache', '-v', '/home/patchew2/.cache/qemu-docker-ccache:/var/tmp/ccache:z', '-v', '/var/tmp/patchew-tester-tmp-y2quzqfb/src/docker-src.2020-07-01-12.41.12.23538:/var/tmp/qemu:z,ro', 'qemu:centos7', '/var/tmp/qemu/run', 'test-quick']' returned non-zero exit status 2.
filter=--filter=label=com.qemu.instance.uuid=67228a70e7844d70b07a864fef5c4569
make[1]: *** [docker-run] Error 1
make[1]: Leaving directory `/var/tmp/patchew-tester-tmp-y2quzqfb/src'
make: *** [docker-run-test-quick@centos7] Error 2

real    17m41.892s
user    0m5.790s


The full log is available at
http://patchew.org/logs/20200701160509.1523847-1-berrange@redhat.com/testing.docker-quick@centos7/?type=message.
---
Email generated automatically by Patchew [https://patchew.org/].
Please send your feedback to patchew-devel@redhat.com

Re: [PATCH 2/3] util: support detailed error reporting for qemu_open

[Markus Armbruster]

Daniel P. Berrangé <berrange@redhat.com> writes:

> Create a "qemu_open_err" method which does the same as "qemu_open",
> but with a "Error **errp" for error reporting. There should be no
> behavioural difference for existing callers at this stage.
>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  include/qemu/osdep.h |  1 +
>  util/osdep.c         | 71 +++++++++++++++++++++++++++++++++++---------
>  2 files changed, 58 insertions(+), 14 deletions(-)
>
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 0d26a1b9bd..e41701a308 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -483,6 +483,7 @@ int qemu_madvise(void *addr, size_t len, int advice);
>  int qemu_mprotect_rwx(void *addr, size_t size);
>  int qemu_mprotect_none(void *addr, size_t size);
>  
> +int qemu_open_err(const char *name, int flags, Error **errp, ...);
>  int qemu_open(const char *name, int flags, ...);
>  int qemu_close(int fd);
>  int qemu_unlink(const char *name);
> diff --git a/util/osdep.c b/util/osdep.c
> index 4bdbe81cec..450b3a5da3 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -22,6 +22,7 @@
>   * THE SOFTWARE.
>   */
>  #include "qemu/osdep.h"
> +#include "qapi/error.h"
>  
>  /* Needed early for CONFIG_BSD etc. */
>  
> @@ -282,7 +283,7 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
>  /*
>   * Opens a file with FD_CLOEXEC set
>   */
> -int qemu_open(const char *name, int flags, ...)
> +static int qemu_openv(const char *name, int flags, Error **errp, va_list ap)
>  {
>      int ret;
>      int mode = 0;
> @@ -297,24 +298,31 @@ int qemu_open(const char *name, int flags, ...)
>  
>          fdset_id = qemu_parse_fdset(fdset_id_str);
>          if (fdset_id == -1) {
> +            error_setg(errp, "Unable to parse fdset %s", name);
>              errno = EINVAL;
>              return -1;
>          }
>  
>          fd = monitor_fdset_get_fd(fdset_id, flags);
>          if (fd < 0) {
> +            error_setg_errno(errp, -fd, "Unable acquire FD for %s flags %x",
> +                             name, flags);
>              errno = -fd;
>              return -1;
>          }
>  
>          dupfd = qemu_dup_flags(fd, flags);
>          if (dupfd == -1) {
> +            error_setg_errno(errp, errno, "Unable dup FD for %s flags %x",
> +                             name, flags);
>              return -1;
>          }
>  
>          ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
>          if (ret == -1) {
>              close(dupfd);
> +            error_setg(errp, "Unable save FD for %s flags %x",
> +                       name, flags);
>              errno = EINVAL;
>              return -1;
>          }
> @@ -324,11 +332,7 @@ int qemu_open(const char *name, int flags, ...)
>  #endif
>  
>      if (flags & O_CREAT) {
> -        va_list ap;
> -
> -        va_start(ap, flags);
>          mode = va_arg(ap, int);
> -        va_end(ap);
>      }
>  
>  #ifdef O_CLOEXEC
> @@ -340,25 +344,64 @@ int qemu_open(const char *name, int flags, ...)
>      }
>  #endif
>  
> +    if (ret == -1) {
> +        const char *action = "open";
> +        if (flags & O_CREAT) {
> +            action = "create";
> +        }
>  #ifdef O_DIRECT
> -    if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
> -        int newflags = flags & ~O_DIRECT;
> +        if (errno == EINVAL && (flags & O_DIRECT)) {
> +            int newflags = flags & ~O_DIRECT;
>  # ifdef O_CLOEXEC
> -        ret = open(name, newflags | O_CLOEXEC, mode);
> +            ret = open(name, newflags | O_CLOEXEC, mode);
>  # else
> -        ret = open(name, newflags, mode);
> +            ret = open(name, newflags, mode);
>  # endif
> -        if (ret != -1) {
> -            close(ret);
> -            error_report("file system does not support O_DIRECT");
> -            errno = EINVAL;
> +            if (ret != -1) {
> +                close(ret);
> +                error_setg(errp, "Unable to %s '%s' flags 0x%x: "
> +                           "filesystem does not support O_DIRECT",
> +                           action, name, flags);
> +                if (!errp) {

If the caller ignores errors, ...

> +                    error_report("file system does not support O_DIRECT");

... we report this error to stderr (but not any of the other ones).
This is weird.  I figure you do it here to reproduce the weirdness of
qemu_open() before the patch.  Goes back to

    commit a5813077aac7865f69b7ee46a594f3705429f7cd
    Author: Stefan Hajnoczi <stefanha@redhat.com>
    Date:   Thu Aug 22 11:29:03 2013 +0200

        osdep: warn if open(O_DIRECT) on fails with EINVAL

        Print a warning when opening a file O_DIRECT fails with EINVAL.  This
        saves users a lot of time trying to figure out the EINVAL error, which
        is typical when attempting to open a file O_DIRECT on Linux tmpfs.

        Reported-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>
        Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
        Reviewed-by: Eric Blake <eblake@redhat.com>

The message isn't phrased as a warning, though.  Should it use
warn_report()?  Stefan?

Regardless, since use of error_report() in a function that returns
errors through its Error ** parameter is an anti-pattern, this use needs
a comment.  I'd make it a TODO comment: convert all callers where the
warning is wanted to qemu_open_err(), then drop it.

> +                }
> +                errno = EINVAL;
> +                return -1;
> +            }
>          }
> -    }
>  #endif /* O_DIRECT */
> +        error_setg_errno(errp, errno, "Unable to %s '%s' flags 0x%x",
> +                         action, name, flags);
> +    }
> +
>  
>      return ret;
>  }
>  
> +int qemu_open_err(const char *name, int flags, Error **errp, ...)
> +{
> +    va_list ap;
> +    int rv;
> +
> +    va_start(ap, errp);
> +    rv = qemu_openv(name, flags, errp, ap);
> +    va_end(ap);
> +
> +    return rv;
> +}
> +
> +int qemu_open(const char *name, int flags, ...)
> +{
> +    va_list ap;
> +    int rv;
> +
> +    va_start(ap, flags);
> +    rv = qemu_openv(name, flags, NULL, ap);
> +    va_end(ap);
> +
> +    return rv;
> +}

I'd rename this to qemu_open_with_bad_error_messages().

For better ones, callers can use

    if (qemu_open_err(name, flags, &err) < 0) {
        error_report_err(err);
        ...
    }

or, where the error is fatal
    
    qemu_open_err(name, flags, &error_fatal);

If you prefer not to rename it now, please add a comment why it should
not be used in new code, and existing uses should be converted.

If you rename, call the new one qemu_open().

> +
>  int qemu_close(int fd)
>  {
>      int64_t fdset_id;

Re: [PATCH 2/3] util: support detailed error reporting for qemu_open

[Daniel P. Berrangé]

On Thu, Jul 02, 2020 at 07:13:08AM +0200, Markus Armbruster wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
> 
> > Create a "qemu_open_err" method which does the same as "qemu_open",
> > but with a "Error **errp" for error reporting. There should be no
> > behavioural difference for existing callers at this stage.
> >
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >  include/qemu/osdep.h |  1 +
> >  util/osdep.c         | 71 +++++++++++++++++++++++++++++++++++---------
> >  2 files changed, 58 insertions(+), 14 deletions(-)
> >
> > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > index 0d26a1b9bd..e41701a308 100644
> > --- a/include/qemu/osdep.h
> > +++ b/include/qemu/osdep.h
> > @@ -483,6 +483,7 @@ int qemu_madvise(void *addr, size_t len, int advice);
> >  int qemu_mprotect_rwx(void *addr, size_t size);
> >  int qemu_mprotect_none(void *addr, size_t size);
> >  
> > +int qemu_open_err(const char *name, int flags, Error **errp, ...);
> >  int qemu_open(const char *name, int flags, ...);
> >  int qemu_close(int fd);
> >  int qemu_unlink(const char *name);
> > diff --git a/util/osdep.c b/util/osdep.c
> > index 4bdbe81cec..450b3a5da3 100644
> > --- a/util/osdep.c
> > +++ b/util/osdep.c
> > @@ -22,6 +22,7 @@
> >   * THE SOFTWARE.
> >   */
> >  #include "qemu/osdep.h"
> > +#include "qapi/error.h"
> >  
> >  /* Needed early for CONFIG_BSD etc. */
> >  
> > @@ -282,7 +283,7 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
> >  /*
> >   * Opens a file with FD_CLOEXEC set
> >   */
> > -int qemu_open(const char *name, int flags, ...)
> > +static int qemu_openv(const char *name, int flags, Error **errp, va_list ap)
> >  {
> >      int ret;
> >      int mode = 0;
> > @@ -297,24 +298,31 @@ int qemu_open(const char *name, int flags, ...)
> >  
> >          fdset_id = qemu_parse_fdset(fdset_id_str);
> >          if (fdset_id == -1) {
> > +            error_setg(errp, "Unable to parse fdset %s", name);
> >              errno = EINVAL;
> >              return -1;
> >          }
> >  
> >          fd = monitor_fdset_get_fd(fdset_id, flags);
> >          if (fd < 0) {
> > +            error_setg_errno(errp, -fd, "Unable acquire FD for %s flags %x",
> > +                             name, flags);
> >              errno = -fd;
> >              return -1;
> >          }
> >  
> >          dupfd = qemu_dup_flags(fd, flags);
> >          if (dupfd == -1) {
> > +            error_setg_errno(errp, errno, "Unable dup FD for %s flags %x",
> > +                             name, flags);
> >              return -1;
> >          }
> >  
> >          ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
> >          if (ret == -1) {
> >              close(dupfd);
> > +            error_setg(errp, "Unable save FD for %s flags %x",
> > +                       name, flags);
> >              errno = EINVAL;
> >              return -1;
> >          }
> > @@ -324,11 +332,7 @@ int qemu_open(const char *name, int flags, ...)
> >  #endif
> >  
> >      if (flags & O_CREAT) {
> > -        va_list ap;
> > -
> > -        va_start(ap, flags);
> >          mode = va_arg(ap, int);
> > -        va_end(ap);
> >      }
> >  
> >  #ifdef O_CLOEXEC
> > @@ -340,25 +344,64 @@ int qemu_open(const char *name, int flags, ...)
> >      }
> >  #endif
> >  
> > +    if (ret == -1) {
> > +        const char *action = "open";
> > +        if (flags & O_CREAT) {
> > +            action = "create";
> > +        }
> >  #ifdef O_DIRECT
> > -    if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
> > -        int newflags = flags & ~O_DIRECT;
> > +        if (errno == EINVAL && (flags & O_DIRECT)) {
> > +            int newflags = flags & ~O_DIRECT;
> >  # ifdef O_CLOEXEC
> > -        ret = open(name, newflags | O_CLOEXEC, mode);
> > +            ret = open(name, newflags | O_CLOEXEC, mode);
> >  # else
> > -        ret = open(name, newflags, mode);
> > +            ret = open(name, newflags, mode);
> >  # endif
> > -        if (ret != -1) {
> > -            close(ret);
> > -            error_report("file system does not support O_DIRECT");
> > -            errno = EINVAL;
> > +            if (ret != -1) {
> > +                close(ret);
> > +                error_setg(errp, "Unable to %s '%s' flags 0x%x: "
> > +                           "filesystem does not support O_DIRECT",
> > +                           action, name, flags);
> > +                if (!errp) {
> 
> If the caller ignores errors, ...
> 
> > +                    error_report("file system does not support O_DIRECT");
> 
> ... we report this error to stderr (but not any of the other ones).
> This is weird.  I figure you do it here to reproduce the weirdness of
> qemu_open() before the patch.  Goes back to
> 
>     commit a5813077aac7865f69b7ee46a594f3705429f7cd
>     Author: Stefan Hajnoczi <stefanha@redhat.com>
>     Date:   Thu Aug 22 11:29:03 2013 +0200
> 
>         osdep: warn if open(O_DIRECT) on fails with EINVAL
> 
>         Print a warning when opening a file O_DIRECT fails with EINVAL.  This
>         saves users a lot of time trying to figure out the EINVAL error, which
>         is typical when attempting to open a file O_DIRECT on Linux tmpfs.
> 
>         Reported-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>
>         Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>         Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> The message isn't phrased as a warning, though.  Should it use
> warn_report()?  Stefan?

I was really in two minds as to whether to keep this error_report or
not. It depends depends on whether any other callers of qemu_open
still need it. In fact if nothing outside the block layer uses O_DIRECT
then I think we can remove the error_report line.


> > +int qemu_open_err(const char *name, int flags, Error **errp, ...)
> > +{
> > +    va_list ap;
> > +    int rv;
> > +
> > +    va_start(ap, errp);
> > +    rv = qemu_openv(name, flags, errp, ap);
> > +    va_end(ap);
> > +
> > +    return rv;
> > +}
> > +
> > +int qemu_open(const char *name, int flags, ...)
> > +{
> > +    va_list ap;
> > +    int rv;
> > +
> > +    va_start(ap, flags);
> > +    rv = qemu_openv(name, flags, NULL, ap);
> > +    va_end(ap);
> > +
> > +    return rv;
> > +}
> 
> I'd rename this to qemu_open_with_bad_error_messages().

My goal was to avoid a big bang conversion of all callers.

> 
> For better ones, callers can use
> 
>     if (qemu_open_err(name, flags, &err) < 0) {
>         error_report_err(err);
>         ...
>     }
> 
> or, where the error is fatal
>     
>     qemu_open_err(name, flags, &error_fatal);
> 
> If you prefer not to rename it now, please add a comment why it should
> not be used in new code, and existing uses should be converted.
> 
> If you rename, call the new one qemu_open().

Maybe it is better to rename upfront though, instead of waiting till
everything uses the qemu_open_err and then renaming back to qemu_open.

Regards,
Daniel
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Re: [PATCH 1/3] util: validate whether O_DIRECT is supported after failure

[Philippe Mathieu-Daudé]

On 7/1/20 6:05 PM, Daniel P. Berrangé wrote:
> Currently we suggest that a filesystem may not support O_DIRECT after
> seeing an EINVAL. Other things can cause EINVAL though, so it is better
> to do an explicit check, and then report a definitive error message.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  util/osdep.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/util/osdep.c b/util/osdep.c
> index 4829c07ff6..4bdbe81cec 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -342,8 +342,17 @@ int qemu_open(const char *name, int flags, ...)
>  
>  #ifdef O_DIRECT
>      if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
> -        error_report("file system may not support O_DIRECT");
> -        errno = EINVAL; /* in case it was clobbered */
> +        int newflags = flags & ~O_DIRECT;
> +# ifdef O_CLOEXEC
> +        ret = open(name, newflags | O_CLOEXEC, mode);
> +# else
> +        ret = open(name, newflags, mode);
> +# endif

Can we use this simpler form (easier to set a breakpoint)?

   #ifdef O_CLOEXEC
           newflags |= O_CLOEXEC;
   #endif
           ret = open(name, newflags, mode);

Whichever you prefer:
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> +        if (ret != -1) {
> +            close(ret);
> +            error_report("file system does not support O_DIRECT");
> +            errno = EINVAL;
> +        }
>      }
>  #endif /* O_DIRECT */
>  
>