[PATCH] xen: write information about supported backends

[PATCH] xen: write information about supported backends

[Juergen Gross]

Add a Xenstore directory for each supported pv backend. This will allow
Xen tools to decide which backend type to use in case there are
multiple possibilities.

The information is added under
/local/domain/<backend-domid>/device-model/<domid>/backends
before the "running" state is written to Xenstore. Using a directory
for each directory enables us to add parameters for specific backends
in the future.

In order to reuse the Xenstore directory creation already present in
hw/xen/xen_devconfig.c move the related functions to
hw/xen/xen_backend.c where they fit better.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 hw/xen/xen_backend.c         | 52 ++++++++++++++++++++++++++++++++++++++++++++
 hw/xen/xen_devconfig.c       | 52 ++------------------------------------------
 include/hw/xen/xen_backend.h |  1 +
 3 files changed, 55 insertions(+), 50 deletions(-)

diff --git a/hw/xen/xen_backend.c b/hw/xen/xen_backend.c
index 60575ad..8983440 100644
--- a/hw/xen/xen_backend.c
+++ b/hw/xen/xen_backend.c
@@ -42,11 +42,35 @@ struct xs_handle *xenstore = NULL;
 const char *xen_protocol;
 
 /* private */
+struct xs_dirs {
+    char *xs_dir;
+    QTAILQ_ENTRY(xs_dirs) list;
+};
+static QTAILQ_HEAD(xs_dirs_head, xs_dirs) xs_cleanup = QTAILQ_HEAD_INITIALIZER(xs_cleanup);
+
 static QTAILQ_HEAD(XenDeviceHead, XenDevice) xendevs = QTAILQ_HEAD_INITIALIZER(xendevs);
 static int debug = 0;
 
 /* ------------------------------------------------------------- */
 
+static void xenstore_cleanup_dir(char *dir)
+{
+    struct xs_dirs *d;
+
+    d = g_malloc(sizeof(*d));
+    d->xs_dir = dir;
+    QTAILQ_INSERT_TAIL(&xs_cleanup, d, list);
+}
+
+void xen_config_cleanup(void)
+{
+    struct xs_dirs *d;
+
+    QTAILQ_FOREACH(d, &xs_cleanup, list) {
+        xs_rm(xenstore, 0, d->xs_dir);
+    }
+}
+
 int xenstore_write_str(const char *base, const char *node, const char *val)
 {
     char abspath[XEN_BUFSIZE];
@@ -75,6 +99,28 @@ char *xenstore_read_str(const char *base, const char *node)
     return ret;
 }
 
+int xenstore_mkdir(char *path, int p)
+{
+    struct xs_permissions perms[2] = {{
+            .id    = 0, /* set owner: dom0 */
+        },{
+            .id    = xen_domid,
+            .perms = p,
+        }};
+
+    if (!xs_mkdir(xenstore, 0, path)) {
+        xen_be_printf(NULL, 0, "xs_mkdir %s: failed\n", path);
+        return -1;
+    }
+    xenstore_cleanup_dir(g_strdup(path));
+
+    if (!xs_set_permissions(xenstore, 0, path, perms, 2)) {
+        xen_be_printf(NULL, 0, "xs_set_permissions %s: failed\n", path);
+        return -1;
+    }
+    return 0;
+}
+
 int xenstore_write_int(const char *base, const char *node, int ival)
 {
     char val[12];
@@ -726,6 +772,12 @@ err:
 
 int xen_be_register(const char *type, struct XenDevOps *ops)
 {
+    char path[50];
+
+    snprintf(path, sizeof (path), "device-model/%u/backends/%s", xen_domid,
+             type);
+    xenstore_mkdir(path, XS_PERM_READ);
+
     return xenstore_scan(type, xen_domid, ops);
 }
 
diff --git a/hw/xen/xen_devconfig.c b/hw/xen/xen_devconfig.c
index 1f30fe4..b7d290d 100644
--- a/hw/xen/xen_devconfig.c
+++ b/hw/xen/xen_devconfig.c
@@ -5,54 +5,6 @@
 
 /* ------------------------------------------------------------- */
 
-struct xs_dirs {
-    char *xs_dir;
-    QTAILQ_ENTRY(xs_dirs) list;
-};
-static QTAILQ_HEAD(xs_dirs_head, xs_dirs) xs_cleanup = QTAILQ_HEAD_INITIALIZER(xs_cleanup);
-
-static void xen_config_cleanup_dir(char *dir)
-{
-    struct xs_dirs *d;
-
-    d = g_malloc(sizeof(*d));
-    d->xs_dir = dir;
-    QTAILQ_INSERT_TAIL(&xs_cleanup, d, list);
-}
-
-void xen_config_cleanup(void)
-{
-    struct xs_dirs *d;
-
-    QTAILQ_FOREACH(d, &xs_cleanup, list) {
-	xs_rm(xenstore, 0, d->xs_dir);
-    }
-}
-
-/* ------------------------------------------------------------- */
-
-static int xen_config_dev_mkdir(char *dev, int p)
-{
-    struct xs_permissions perms[2] = {{
-            .id    = 0, /* set owner: dom0 */
-        },{
-            .id    = xen_domid,
-            .perms = p,
-        }};
-
-    if (!xs_mkdir(xenstore, 0, dev)) {
-	xen_be_printf(NULL, 0, "xs_mkdir %s: failed\n", dev);
-	return -1;
-    }
-    xen_config_cleanup_dir(g_strdup(dev));
-
-    if (!xs_set_permissions(xenstore, 0, dev, perms, 2)) {
-	xen_be_printf(NULL, 0, "xs_set_permissions %s: failed\n", dev);
-	return -1;
-    }
-    return 0;
-}
-
 static int xen_config_dev_dirs(const char *ftype, const char *btype, int vdev,
 			       char *fe, char *be, int len)
 {
@@ -66,8 +18,8 @@ static int xen_config_dev_dirs(const char *ftype, const char *btype, int vdev,
     snprintf(be, len, "%s/backend/%s/%d/%d", dom, btype, xen_domid, vdev);
     free(dom);
 
-    xen_config_dev_mkdir(fe, XS_PERM_READ | XS_PERM_WRITE);
-    xen_config_dev_mkdir(be, XS_PERM_READ);
+    xenstore_mkdir(fe, XS_PERM_READ | XS_PERM_WRITE);
+    xenstore_mkdir(be, XS_PERM_READ);
     return 0;
 }
 
diff --git a/include/hw/xen/xen_backend.h b/include/hw/xen/xen_backend.h
index b4b4ff0..1bc5042 100644
--- a/include/hw/xen/xen_backend.h
+++ b/include/hw/xen/xen_backend.h
@@ -63,6 +63,7 @@ extern const char *xen_protocol;
 extern DeviceState *xen_sysdev;
 
 /* xenstore helper functions */
+int xenstore_mkdir(char *path, int p);
 int xenstore_write_str(const char *base, const char *node, const char *val);
 int xenstore_write_int(const char *base, const char *node, int ival);
 int xenstore_write_int64(const char *base, const char *node, int64_t ival);
-- 
2.6.2

Re: [PATCH] xen: write information about supported backends

[Stefano Stabellini]

On Wed, 30 Mar 2016, Juergen Gross wrote:
> Add a Xenstore directory for each supported pv backend. This will allow
> Xen tools to decide which backend type to use in case there are
> multiple possibilities.
> 
> The information is added under
> /local/domain/<backend-domid>/device-model/<domid>/backends
> before the "running" state is written to Xenstore. Using a directory
> for each directory enables us to add parameters for specific backends
> in the future.
> 
> In order to reuse the Xenstore directory creation already present in
> hw/xen/xen_devconfig.c move the related functions to
> hw/xen/xen_backend.c where they fit better.

An interface change like this one, needs a new file under docs (in the
Xen repository) to document it.  Please add a reference to it, in the
commit message here.

In addition please make sure that this can work with QEMU running as
non-root. What are the permissions of the new xenstore directory?


> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  hw/xen/xen_backend.c         | 52 ++++++++++++++++++++++++++++++++++++++++++++
>  hw/xen/xen_devconfig.c       | 52 ++------------------------------------------
>  include/hw/xen/xen_backend.h |  1 +
>  3 files changed, 55 insertions(+), 50 deletions(-)
> 
> diff --git a/hw/xen/xen_backend.c b/hw/xen/xen_backend.c
> index 60575ad..8983440 100644
> --- a/hw/xen/xen_backend.c
> +++ b/hw/xen/xen_backend.c
> @@ -42,11 +42,35 @@ struct xs_handle *xenstore = NULL;
>  const char *xen_protocol;
>  
>  /* private */
> +struct xs_dirs {
> +    char *xs_dir;
> +    QTAILQ_ENTRY(xs_dirs) list;
> +};
> +static QTAILQ_HEAD(xs_dirs_head, xs_dirs) xs_cleanup = QTAILQ_HEAD_INITIALIZER(xs_cleanup);
> +
>  static QTAILQ_HEAD(XenDeviceHead, XenDevice) xendevs = QTAILQ_HEAD_INITIALIZER(xendevs);
>  static int debug = 0;
>  
>  /* ------------------------------------------------------------- */
>  
> +static void xenstore_cleanup_dir(char *dir)
> +{
> +    struct xs_dirs *d;
> +
> +    d = g_malloc(sizeof(*d));
> +    d->xs_dir = dir;
> +    QTAILQ_INSERT_TAIL(&xs_cleanup, d, list);
> +}
> +
> +void xen_config_cleanup(void)
> +{
> +    struct xs_dirs *d;
> +
> +    QTAILQ_FOREACH(d, &xs_cleanup, list) {
> +        xs_rm(xenstore, 0, d->xs_dir);
> +    }
> +}
> +
>  int xenstore_write_str(const char *base, const char *node, const char *val)
>  {
>      char abspath[XEN_BUFSIZE];
> @@ -75,6 +99,28 @@ char *xenstore_read_str(const char *base, const char *node)
>      return ret;
>  }
>  
> +int xenstore_mkdir(char *path, int p)
> +{
> +    struct xs_permissions perms[2] = {{
> +            .id    = 0, /* set owner: dom0 */
> +        },{
> +            .id    = xen_domid,
> +            .perms = p,
> +        }};
> +
> +    if (!xs_mkdir(xenstore, 0, path)) {
> +        xen_be_printf(NULL, 0, "xs_mkdir %s: failed\n", path);
> +        return -1;
> +    }
> +    xenstore_cleanup_dir(g_strdup(path));
> +
> +    if (!xs_set_permissions(xenstore, 0, path, perms, 2)) {
> +        xen_be_printf(NULL, 0, "xs_set_permissions %s: failed\n", path);
> +        return -1;
> +    }
> +    return 0;
> +}
> +
>  int xenstore_write_int(const char *base, const char *node, int ival)
>  {
>      char val[12];
> @@ -726,6 +772,12 @@ err:
>  
>  int xen_be_register(const char *type, struct XenDevOps *ops)
>  {
> +    char path[50];
> +
> +    snprintf(path, sizeof (path), "device-model/%u/backends/%s", xen_domid,
> +             type);
> +    xenstore_mkdir(path, XS_PERM_READ);
> +
>      return xenstore_scan(type, xen_domid, ops);
>  }
>  
> diff --git a/hw/xen/xen_devconfig.c b/hw/xen/xen_devconfig.c
> index 1f30fe4..b7d290d 100644
> --- a/hw/xen/xen_devconfig.c
> +++ b/hw/xen/xen_devconfig.c
> @@ -5,54 +5,6 @@
>  
>  /* ------------------------------------------------------------- */
>  
> -struct xs_dirs {
> -    char *xs_dir;
> -    QTAILQ_ENTRY(xs_dirs) list;
> -};
> -static QTAILQ_HEAD(xs_dirs_head, xs_dirs) xs_cleanup = QTAILQ_HEAD_INITIALIZER(xs_cleanup);
> -
> -static void xen_config_cleanup_dir(char *dir)
> -{
> -    struct xs_dirs *d;
> -
> -    d = g_malloc(sizeof(*d));
> -    d->xs_dir = dir;
> -    QTAILQ_INSERT_TAIL(&xs_cleanup, d, list);
> -}
> -
> -void xen_config_cleanup(void)
> -{
> -    struct xs_dirs *d;
> -
> -    QTAILQ_FOREACH(d, &xs_cleanup, list) {
> -	xs_rm(xenstore, 0, d->xs_dir);
> -    }
> -}
> -
> -/* ------------------------------------------------------------- */
> -
> -static int xen_config_dev_mkdir(char *dev, int p)
> -{
> -    struct xs_permissions perms[2] = {{
> -            .id    = 0, /* set owner: dom0 */
> -        },{
> -            .id    = xen_domid,
> -            .perms = p,
> -        }};
> -
> -    if (!xs_mkdir(xenstore, 0, dev)) {
> -	xen_be_printf(NULL, 0, "xs_mkdir %s: failed\n", dev);
> -	return -1;
> -    }
> -    xen_config_cleanup_dir(g_strdup(dev));
> -
> -    if (!xs_set_permissions(xenstore, 0, dev, perms, 2)) {
> -	xen_be_printf(NULL, 0, "xs_set_permissions %s: failed\n", dev);
> -	return -1;
> -    }
> -    return 0;
> -}
> -
>  static int xen_config_dev_dirs(const char *ftype, const char *btype, int vdev,
>  			       char *fe, char *be, int len)
>  {
> @@ -66,8 +18,8 @@ static int xen_config_dev_dirs(const char *ftype, const char *btype, int vdev,
>      snprintf(be, len, "%s/backend/%s/%d/%d", dom, btype, xen_domid, vdev);
>      free(dom);
>  
> -    xen_config_dev_mkdir(fe, XS_PERM_READ | XS_PERM_WRITE);
> -    xen_config_dev_mkdir(be, XS_PERM_READ);
> +    xenstore_mkdir(fe, XS_PERM_READ | XS_PERM_WRITE);
> +    xenstore_mkdir(be, XS_PERM_READ);
>      return 0;
>  }
>  
> diff --git a/include/hw/xen/xen_backend.h b/include/hw/xen/xen_backend.h
> index b4b4ff0..1bc5042 100644
> --- a/include/hw/xen/xen_backend.h
> +++ b/include/hw/xen/xen_backend.h
> @@ -63,6 +63,7 @@ extern const char *xen_protocol;
>  extern DeviceState *xen_sysdev;
>  
>  /* xenstore helper functions */
> +int xenstore_mkdir(char *path, int p);
>  int xenstore_write_str(const char *base, const char *node, const char *val);
>  int xenstore_write_int(const char *base, const char *node, int ival);
>  int xenstore_write_int64(const char *base, const char *node, int64_t ival);
> -- 
> 2.6.2
> 

Re: [PATCH] xen: write information about supported backends

[Juergen Gross]

On 01/04/16 16:56, Stefano Stabellini wrote:
> On Wed, 30 Mar 2016, Juergen Gross wrote:
>> Add a Xenstore directory for each supported pv backend. This will allow
>> Xen tools to decide which backend type to use in case there are
>> multiple possibilities.
>>
>> The information is added under
>> /local/domain/<backend-domid>/device-model/<domid>/backends
>> before the "running" state is written to Xenstore. Using a directory
>> for each directory enables us to add parameters for specific backends
>> in the future.
>>
>> In order to reuse the Xenstore directory creation already present in
>> hw/xen/xen_devconfig.c move the related functions to
>> hw/xen/xen_backend.c where they fit better.
> 
> An interface change like this one, needs a new file under docs (in the
> Xen repository) to document it.  Please add a reference to it, in the
> commit message here.

Is the Xenstore path documentation enough? Or do you want something
like docs/misc/qemu-deprivilege.txt to be added?

> In addition please make sure that this can work with QEMU running as
> non-root. What are the permissions of the new xenstore directory?

Should work, as I'm using the same functions as any backend in qemu is
using. The new directory is read-only for the qemu target domain (same
as the backend directories).


Juergen

Re: [Xen-devel] [PATCH] xen: write information about supported backends

[David Vrabel]

On 30/03/16 15:10, Juergen Gross wrote:
> Add a Xenstore directory for each supported pv backend. This will allow
> Xen tools to decide which backend type to use in case there are
> multiple possibilities.
> 
> The information is added under
> /local/domain/<backend-domid>/device-model/<domid>/backends
> before the "running" state is written to Xenstore. Using a directory
> for each directory enables us to add parameters for specific backends
> in the future.

"Using a directory for each backend..."?
> 
> In order to reuse the Xenstore directory creation already present in
> hw/xen/xen_devconfig.c move the related functions to
> hw/xen/xen_backend.c where they fit better.

Why Xenstore and not QMP?

David

Re: [Xen-devel] [PATCH] xen: write information about supported backends

[Juergen Gross]

On 04/04/16 11:18, David Vrabel wrote:
> On 30/03/16 15:10, Juergen Gross wrote:
>> Add a Xenstore directory for each supported pv backend. This will allow
>> Xen tools to decide which backend type to use in case there are
>> multiple possibilities.
>>
>> The information is added under
>> /local/domain/<backend-domid>/device-model/<domid>/backends
>> before the "running" state is written to Xenstore. Using a directory
>> for each directory enables us to add parameters for specific backends
>> in the future.
> 
> "Using a directory for each backend..."?

Yes. As I've written: this enables us to enhance the interface later
without the need to modify it first.

>> In order to reuse the Xenstore directory creation already present in
>> hw/xen/xen_devconfig.c move the related functions to
>> hw/xen/xen_backend.c where they fit better.
> 
> Why Xenstore and not QMP?

We need to communicate with qemu only once instead of each time a
device is added to the domain. Doing the communication via Xenstore
is much simpler.

Juergen

Re: [PATCH] xen: write information about supported backends

[Stefano Stabellini]

On Mon, 4 Apr 2016, Juergen Gross wrote:
> On 01/04/16 16:56, Stefano Stabellini wrote:
> > On Wed, 30 Mar 2016, Juergen Gross wrote:
> >> Add a Xenstore directory for each supported pv backend. This will allow
> >> Xen tools to decide which backend type to use in case there are
> >> multiple possibilities.
> >>
> >> The information is added under
> >> /local/domain/<backend-domid>/device-model/<domid>/backends
> >> before the "running" state is written to Xenstore. Using a directory
> >> for each directory enables us to add parameters for specific backends
> >> in the future.
> >>
> >> In order to reuse the Xenstore directory creation already present in
> >> hw/xen/xen_devconfig.c move the related functions to
> >> hw/xen/xen_backend.c where they fit better.
> > 
> > An interface change like this one, needs a new file under docs (in the
> > Xen repository) to document it.  Please add a reference to it, in the
> > commit message here.
> 
> Is the Xenstore path documentation enough? Or do you want something
> like docs/misc/qemu-deprivilege.txt to be added?

Something like qemu-deprivilege.txt would be acceptable.


> > In addition please make sure that this can work with QEMU running as
> > non-root. What are the permissions of the new xenstore directory?
> 
> Should work, as I'm using the same functions as any backend in qemu is
> using. The new directory is read-only for the qemu target domain (same
> as the backend directories).

All right, just make sure to have xen-qemuuser-shared or
xen-qemuuser-domid on your system when you test :-)