[v2] block: Add auto-read-only option

[Qemu-devel] [PATCH v2 7/8] gluster: Support auto-read-only option

Posted by Kevin Wolf 7 years ago

If read-only=off, but auto-read-only=on is given, open the file
read-write if we have the permissions, but instead of erroring out for
read-only files, just degrade to read-only.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/gluster.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/block/gluster.c b/block/gluster.c
index 4fd55a9cc5..68d20c8830 100644
--- a/block/gluster.c
+++ b/block/gluster.c
@@ -849,6 +849,15 @@ static int qemu_gluster_open(BlockDriverState *bs,  QDict *options,
     qemu_gluster_parse_flags(bdrv_flags, &open_flags);
 
     s->fd = glfs_open(s->glfs, gconf->path, open_flags);
+    if (!s->fd && errno == EACCES) {
+        /* Try to degrade to read-only, but if it doesn't work, still use the
+         * normal error message. */
+        ret = bdrv_apply_auto_read_only(bs, NULL, NULL);
+        if (ret == 0) {
+            open_flags = (open_flags & ~O_RDWR) | O_RDONLY;
+            s->fd = glfs_open(s->glfs, gconf->path, open_flags);
+        }
+    }
     if (!s->fd) {
         ret = -errno;
     }
-- 
2.19.1

Re: [Qemu-devel] [PATCH v2 7/8] gluster: Support auto-read-only option

Posted by Eric Blake 7 years ago

On 10/12/18 6:55 AM, Kevin Wolf wrote:
> If read-only=off, but auto-read-only=on is given, open the file
> read-write if we have the permissions, but instead of erroring out for
> read-only files, just degrade to read-only.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   block/gluster.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/block/gluster.c b/block/gluster.c
> index 4fd55a9cc5..68d20c8830 100644
> --- a/block/gluster.c
> +++ b/block/gluster.c
> @@ -849,6 +849,15 @@ static int qemu_gluster_open(BlockDriverState *bs,  QDict *options,
>       qemu_gluster_parse_flags(bdrv_flags, &open_flags);
>   
>       s->fd = glfs_open(s->glfs, gconf->path, open_flags);
> +    if (!s->fd && errno == EACCES) {

EROFS is not possible as it was for posix file?

> +        /* Try to degrade to read-only, but if it doesn't work, still use the
> +         * normal error message. */
> +        ret = bdrv_apply_auto_read_only(bs, NULL, NULL);

No guarantees on what errno is on failure...

> +        if (ret == 0) {
> +            open_flags = (open_flags & ~O_RDWR) | O_RDONLY;
> +            s->fd = glfs_open(s->glfs, gconf->path, open_flags);
> +        }
> +    }
>       if (!s->fd) {
>           ret = -errno;

...but you are relying on it here.  (Same story as in the posix driver)

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [Qemu-block] [PATCH v2 7/8] gluster: Support auto-read-only option

Posted by Niels de Vos 7 years ago

On Fri, Oct 12, 2018 at 12:31:21PM -0500, Eric Blake wrote:
> On 10/12/18 6:55 AM, Kevin Wolf wrote:
> > If read-only=off, but auto-read-only=on is given, open the file
> > read-write if we have the permissions, but instead of erroring out for
> > read-only files, just degrade to read-only.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >   block/gluster.c | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> > 
> > diff --git a/block/gluster.c b/block/gluster.c
> > index 4fd55a9cc5..68d20c8830 100644
> > --- a/block/gluster.c
> > +++ b/block/gluster.c
> > @@ -849,6 +849,15 @@ static int qemu_gluster_open(BlockDriverState *bs,  QDict *options,
> >       qemu_gluster_parse_flags(bdrv_flags, &open_flags);
> >       s->fd = glfs_open(s->glfs, gconf->path, open_flags);
> > +    if (!s->fd && errno == EACCES) {
> 
> EROFS is not possible as it was for posix file?

EROFS can happen, depending on the configuration of the Gluster volume.
In that case, opening read-only should work fine.

Niels