[PATCH 0/2] block/blkio: fix opening virtio-blk drivers

[PATCH 0/2] block/blkio: fix opening virtio-blk drivers

[Stefano Garzarella]

There is a problem with virtio-blk-vhost-vdpa. The first patch
fixes the issue, the second patch tries to prepare QEMU for a
future version of libblkio where we can use blkio_set_fd() to
check whether the property is supported or not.

Stefano Garzarella (2):
  block/blkio: fix opening virtio-blk drivers
  block/blkio: use blkio_set_int("fd") to check fd support

 block/blkio.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

-- 
2.41.0

[PATCH 1/2] block/blkio: fix opening virtio-blk drivers

[Stefano Garzarella]

libblkio 1.3.0 added support of "fd" property for virtio-blk-vhost-vdpa
driver. In QEMU, starting from commit cad2ccc395 ("block/blkio: use
qemu_open() to support fd passing for virtio-blk") we are using
`blkio_get_int(..., "fd")` to check if the "fd" property is supported
for all the virtio-blk-* driver.

Unfortunately that property is also available for those driver that do
not support it, such as virtio-blk-vhost-user. Indeed now QEMU is
failing if used with virtio-blk-vhost-user in this way:

   -blockdev node-name=drive0,driver=virtio-blk-vhost-user,path=vhost-user-blk.sock,cache.direct=on: Could not open 'vhost-user-blk.sock': No such device or address

So, `blkio_get_int()` is not enough to check whether the driver supports
the `fd` property or not. This is because the virito-blk common libblkio
driver only checks whether or not `fd` is set during `blkio_connect()`
and fails for those transports that do not support it (all except
vhost-vdpa for now).

So for now let's also check that the driver is virtio-blk-vhost-vdpa,
since that's the only one that supports it.

Fixes: cad2ccc395 ("block/blkio: use qemu_open() to support fd passing for virtio-blk")
Reported-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 block/blkio.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/blkio.c b/block/blkio.c
index 1798648134..ca1149042a 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -662,6 +662,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
         QDict *options, int flags, Error **errp)
 {
     const char *path = qdict_get_try_str(options, "path");
+    const char *blkio_driver = bs->drv->protocol_name;
     BDRVBlkioState *s = bs->opaque;
     bool fd_supported = false;
     int fd, ret;
@@ -676,7 +677,8 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
         return -EINVAL;
     }
 
-    if (blkio_get_int(s->blkio, "fd", &fd) == 0) {
+    if (strcmp(blkio_driver, "virtio-blk-vhost-vdpa") == 0 &&
+        blkio_get_int(s->blkio, "fd", &fd) == 0) {
         fd_supported = true;
     }
 
-- 
2.41.0

Re: [PATCH 1/2] block/blkio: fix opening virtio-blk drivers

[Stefan Hajnoczi]

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On Mon, Jul 24, 2023 at 05:46:10PM +0200, Stefano Garzarella wrote:
> libblkio 1.3.0 added support of "fd" property for virtio-blk-vhost-vdpa
> driver. In QEMU, starting from commit cad2ccc395 ("block/blkio: use
> qemu_open() to support fd passing for virtio-blk") we are using
> `blkio_get_int(..., "fd")` to check if the "fd" property is supported
> for all the virtio-blk-* driver.
> 
> Unfortunately that property is also available for those driver that do
> not support it, such as virtio-blk-vhost-user. Indeed now QEMU is
> failing if used with virtio-blk-vhost-user in this way:
> 
>    -blockdev node-name=drive0,driver=virtio-blk-vhost-user,path=vhost-user-blk.sock,cache.direct=on: Could not open 'vhost-user-blk.sock': No such device or address
> 
> So, `blkio_get_int()` is not enough to check whether the driver supports
> the `fd` property or not. This is because the virito-blk common libblkio
> driver only checks whether or not `fd` is set during `blkio_connect()`
> and fails for those transports that do not support it (all except
> vhost-vdpa for now).
> 
> So for now let's also check that the driver is virtio-blk-vhost-vdpa,
> since that's the only one that supports it.

What happens when more virtio-blk-* libblkio drivers gain support for
`fd`? I think we'll be back to the same problem because QEMU will be
unable to distinguish between old and new libraries.

How about retrying with `path` if opening with `fd` fails?

> 
> Fixes: cad2ccc395 ("block/blkio: use qemu_open() to support fd passing for virtio-blk")
> Reported-by: Qing Wang <qinwang@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  block/blkio.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blkio.c b/block/blkio.c
> index 1798648134..ca1149042a 100644
> --- a/block/blkio.c
> +++ b/block/blkio.c
> @@ -662,6 +662,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
>          QDict *options, int flags, Error **errp)
>  {
>      const char *path = qdict_get_try_str(options, "path");
> +    const char *blkio_driver = bs->drv->protocol_name;
>      BDRVBlkioState *s = bs->opaque;
>      bool fd_supported = false;
>      int fd, ret;
> @@ -676,7 +677,8 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
>          return -EINVAL;
>      }
>  
> -    if (blkio_get_int(s->blkio, "fd", &fd) == 0) {
> +    if (strcmp(blkio_driver, "virtio-blk-vhost-vdpa") == 0 &&
> +        blkio_get_int(s->blkio, "fd", &fd) == 0) {
>          fd_supported = true;
>      }
>  
> -- 
> 2.41.0
> 

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Re: [PATCH 1/2] block/blkio: fix opening virtio-blk drivers

[Stefano Garzarella]

On Tue, Jul 25, 2023 at 04:00:38PM -0400, Stefan Hajnoczi wrote:
>On Mon, Jul 24, 2023 at 05:46:10PM +0200, Stefano Garzarella wrote:
>> libblkio 1.3.0 added support of "fd" property for virtio-blk-vhost-vdpa
>> driver. In QEMU, starting from commit cad2ccc395 ("block/blkio: use
>> qemu_open() to support fd passing for virtio-blk") we are using
>> `blkio_get_int(..., "fd")` to check if the "fd" property is supported
>> for all the virtio-blk-* driver.
>>
>> Unfortunately that property is also available for those driver that do
>> not support it, such as virtio-blk-vhost-user. Indeed now QEMU is
>> failing if used with virtio-blk-vhost-user in this way:
>>
>>    -blockdev node-name=drive0,driver=virtio-blk-vhost-user,path=vhost-user-blk.sock,cache.direct=on: Could not open 'vhost-user-blk.sock': No such device or address
>>
>> So, `blkio_get_int()` is not enough to check whether the driver supports
>> the `fd` property or not. This is because the virito-blk common libblkio
>> driver only checks whether or not `fd` is set during `blkio_connect()`
>> and fails for those transports that do not support it (all except
>> vhost-vdpa for now).
>>
>> So for now let's also check that the driver is virtio-blk-vhost-vdpa,
>> since that's the only one that supports it.
>
>What happens when more virtio-blk-* libblkio drivers gain support for
>`fd`? I think we'll be back to the same problem because QEMU will be
>unable to distinguish between old and new libraries.

If we release a v1.3.1 version of libblkio with
https://gitlab.com/libblkio/libblkio/-/merge_requests/208
we can set a minimum requirement in QEMU and use blkio_set_fd() here.

>
>How about retrying with `path` if opening with `fd` fails?

IIUC the only way is to check if blkio_connect() will fail with -EINVAL,
that can also be generated by other issues, then retry forcing `path`.

Do you see other ways?

The code wouldn't be great, but we could do it for now and then when
we release a new version of libblkio, do the revert and use
blkio_set_int(fd) to see if it's supported or not.

I don't know if it is worth it, or if it is better to merge this,
release libblkio v1.3.1 and force the minimum requirement.

WDYT?

Thanks,
Stefano

Re: [PATCH 1/2] block/blkio: fix opening virtio-blk drivers

[Stefan Hajnoczi]

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On Wed, Jul 26, 2023 at 09:26:45AM +0200, Stefano Garzarella wrote:
> On Tue, Jul 25, 2023 at 04:00:38PM -0400, Stefan Hajnoczi wrote:
> > On Mon, Jul 24, 2023 at 05:46:10PM +0200, Stefano Garzarella wrote:
> > > libblkio 1.3.0 added support of "fd" property for virtio-blk-vhost-vdpa
> > > driver. In QEMU, starting from commit cad2ccc395 ("block/blkio: use
> > > qemu_open() to support fd passing for virtio-blk") we are using
> > > `blkio_get_int(..., "fd")` to check if the "fd" property is supported
> > > for all the virtio-blk-* driver.
> > > 
> > > Unfortunately that property is also available for those driver that do
> > > not support it, such as virtio-blk-vhost-user. Indeed now QEMU is
> > > failing if used with virtio-blk-vhost-user in this way:
> > > 
> > >    -blockdev node-name=drive0,driver=virtio-blk-vhost-user,path=vhost-user-blk.sock,cache.direct=on: Could not open 'vhost-user-blk.sock': No such device or address
> > > 
> > > So, `blkio_get_int()` is not enough to check whether the driver supports
> > > the `fd` property or not. This is because the virito-blk common libblkio
> > > driver only checks whether or not `fd` is set during `blkio_connect()`
> > > and fails for those transports that do not support it (all except
> > > vhost-vdpa for now).
> > > 
> > > So for now let's also check that the driver is virtio-blk-vhost-vdpa,
> > > since that's the only one that supports it.
> > 
> > What happens when more virtio-blk-* libblkio drivers gain support for
> > `fd`? I think we'll be back to the same problem because QEMU will be
> > unable to distinguish between old and new libraries.
> 
> If we release a v1.3.1 version of libblkio with
> https://gitlab.com/libblkio/libblkio/-/merge_requests/208
> we can set a minimum requirement in QEMU and use blkio_set_fd() here.
> 
> > 
> > How about retrying with `path` if opening with `fd` fails?
> 
> IIUC the only way is to check if blkio_connect() will fail with -EINVAL,
> that can also be generated by other issues, then retry forcing `path`.
> 
> Do you see other ways?

No. Checking for -EINVAL and then retrying with `path` is what I had in
mind.

> The code wouldn't be great, but we could do it for now and then when
> we release a new version of libblkio, do the revert and use
> blkio_set_int(fd) to see if it's supported or not.
> 
> I don't know if it is worth it, or if it is better to merge this,
> release libblkio v1.3.1 and force the minimum requirement.
> 
> WDYT?

I prefer retrying on -EINVAL because even if libblkio 1.3.1 is released
today, we don't have control over when it becomes available in distros.

Stefan

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Re: [PATCH 1/2] block/blkio: fix opening virtio-blk drivers

[Stefano Garzarella]

On Wed, Jul 26, 2023 at 11:32:10AM -0400, Stefan Hajnoczi wrote:
>On Wed, Jul 26, 2023 at 09:26:45AM +0200, Stefano Garzarella wrote:
>> On Tue, Jul 25, 2023 at 04:00:38PM -0400, Stefan Hajnoczi wrote:
>> > On Mon, Jul 24, 2023 at 05:46:10PM +0200, Stefano Garzarella wrote:
>> > > libblkio 1.3.0 added support of "fd" property for virtio-blk-vhost-vdpa
>> > > driver. In QEMU, starting from commit cad2ccc395 ("block/blkio: use
>> > > qemu_open() to support fd passing for virtio-blk") we are using
>> > > `blkio_get_int(..., "fd")` to check if the "fd" property is supported
>> > > for all the virtio-blk-* driver.
>> > >
>> > > Unfortunately that property is also available for those driver that do
>> > > not support it, such as virtio-blk-vhost-user. Indeed now QEMU is
>> > > failing if used with virtio-blk-vhost-user in this way:
>> > >
>> > >    -blockdev node-name=drive0,driver=virtio-blk-vhost-user,path=vhost-user-blk.sock,cache.direct=on: Could not open 'vhost-user-blk.sock': No such device or address
>> > >
>> > > So, `blkio_get_int()` is not enough to check whether the driver supports
>> > > the `fd` property or not. This is because the virito-blk common libblkio
>> > > driver only checks whether or not `fd` is set during `blkio_connect()`
>> > > and fails for those transports that do not support it (all except
>> > > vhost-vdpa for now).
>> > >
>> > > So for now let's also check that the driver is virtio-blk-vhost-vdpa,
>> > > since that's the only one that supports it.
>> >
>> > What happens when more virtio-blk-* libblkio drivers gain support for
>> > `fd`? I think we'll be back to the same problem because QEMU will be
>> > unable to distinguish between old and new libraries.
>>
>> If we release a v1.3.1 version of libblkio with
>> https://gitlab.com/libblkio/libblkio/-/merge_requests/208
>> we can set a minimum requirement in QEMU and use blkio_set_fd() here.
>>
>> >
>> > How about retrying with `path` if opening with `fd` fails?
>>
>> IIUC the only way is to check if blkio_connect() will fail with -EINVAL,
>> that can also be generated by other issues, then retry forcing `path`.
>>
>> Do you see other ways?
>
>No. Checking for -EINVAL and then retrying with `path` is what I had in
>mind.
>
>> The code wouldn't be great, but we could do it for now and then when
>> we release a new version of libblkio, do the revert and use
>> blkio_set_int(fd) to see if it's supported or not.
>>
>> I don't know if it is worth it, or if it is better to merge this,
>> release libblkio v1.3.1 and force the minimum requirement.
>>
>> WDYT?
>
>I prefer retrying on -EINVAL because even if libblkio 1.3.1 is released
>today, we don't have control over when it becomes available in distros.

Fair point!

I'll send v2 using that approach!

Thanks,
Stefano

[PATCH 2/2] block/blkio: use blkio_set_int("fd") to check fd support

[Stefano Garzarella]

The way the virtio-blk driver is implemented in libblkio,
it's much easier to use blkio_set_int() instead of blkio_get_int()
and have it fail right away to see if `fd` is supported by the
transport. See https://gitlab.com/libblkio/libblkio/-/merge_requests/208

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 block/blkio.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/blkio.c b/block/blkio.c
index ca1149042a..719b19324b 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -665,7 +665,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
     const char *blkio_driver = bs->drv->protocol_name;
     BDRVBlkioState *s = bs->opaque;
     bool fd_supported = false;
-    int fd, ret;
+    int ret;
 
     if (!path) {
         error_setg(errp, "missing 'path' option");
@@ -678,7 +678,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
     }
 
     if (strcmp(blkio_driver, "virtio-blk-vhost-vdpa") == 0 &&
-        blkio_get_int(s->blkio, "fd", &fd) == 0) {
+        blkio_set_int(s->blkio, "fd", -1) == 0) {
         fd_supported = true;
     }
 
@@ -688,7 +688,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
      * layer through the "/dev/fdset/N" special path.
      */
     if (fd_supported) {
-        int open_flags;
+        int open_flags, fd;
 
         if (flags & BDRV_O_RDWR) {
             open_flags = O_RDWR;
-- 
2.41.0

Re: [PATCH 2/2] block/blkio: use blkio_set_int("fd") to check fd support

[Stefan Hajnoczi]

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On Mon, Jul 24, 2023 at 05:46:11PM +0200, Stefano Garzarella wrote:
> The way the virtio-blk driver is implemented in libblkio,
> it's much easier to use blkio_set_int() instead of blkio_get_int()
> and have it fail right away to see if `fd` is supported by the
> transport. See https://gitlab.com/libblkio/libblkio/-/merge_requests/208

The commit description is vague about what's going on here. My
understanding is:

  Setting the `fd` property fails with virtio-blk-* libblkio drivers
  that do not support fd passing since
  https://gitlab.com/libblkio/libblkio/-/merge_requests/208.

  Getting the `fd` property, on the other hand, always succeeds for
  virtio-blk-* libblkio drivers even when they don't support fd passing.

  This patch switches to setting the `fd` property because it is a
  better mechanism for probing fd passing support than getting the `fd`
  property.

Please update the commit description. Thanks!

> 
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  block/blkio.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/block/blkio.c b/block/blkio.c
> index ca1149042a..719b19324b 100644
> --- a/block/blkio.c
> +++ b/block/blkio.c
> @@ -665,7 +665,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
>      const char *blkio_driver = bs->drv->protocol_name;
>      BDRVBlkioState *s = bs->opaque;
>      bool fd_supported = false;
> -    int fd, ret;
> +    int ret;
>  
>      if (!path) {
>          error_setg(errp, "missing 'path' option");
> @@ -678,7 +678,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
>      }
>  
>      if (strcmp(blkio_driver, "virtio-blk-vhost-vdpa") == 0 &&
> -        blkio_get_int(s->blkio, "fd", &fd) == 0) {
> +        blkio_set_int(s->blkio, "fd", -1) == 0) {
>          fd_supported = true;
>      }
>  
> @@ -688,7 +688,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
>       * layer through the "/dev/fdset/N" special path.
>       */
>      if (fd_supported) {
> -        int open_flags;
> +        int open_flags, fd;
>  
>          if (flags & BDRV_O_RDWR) {
>              open_flags = O_RDWR;
> -- 
> 2.41.0
> 

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Re: [PATCH 2/2] block/blkio: use blkio_set_int("fd") to check fd support

[Stefano Garzarella]

On Tue, Jul 25, 2023 at 04:05:38PM -0400, Stefan Hajnoczi wrote:
>On Mon, Jul 24, 2023 at 05:46:11PM +0200, Stefano Garzarella wrote:
>> The way the virtio-blk driver is implemented in libblkio,
>> it's much easier to use blkio_set_int() instead of blkio_get_int()
>> and have it fail right away to see if `fd` is supported by the
>> transport. See https://gitlab.com/libblkio/libblkio/-/merge_requests/208
>
>The commit description is vague about what's going on here. My
>understanding is:
>
>  Setting the `fd` property fails with virtio-blk-* libblkio drivers
>  that do not support fd passing since
>  https://gitlab.com/libblkio/libblkio/-/merge_requests/208.
>
>  Getting the `fd` property, on the other hand, always succeeds for
>  virtio-blk-* libblkio drivers even when they don't support fd passing.
>
>  This patch switches to setting the `fd` property because it is a
>  better mechanism for probing fd passing support than getting the `fd`
>  property.
>
>Please update the commit description. Thanks!

Ack, I'll update it.

Thanks,
Stefano

>
>>
>> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>> ---
>>  block/blkio.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/block/blkio.c b/block/blkio.c
>> index ca1149042a..719b19324b 100644
>> --- a/block/blkio.c
>> +++ b/block/blkio.c
>> @@ -665,7 +665,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
>>      const char *blkio_driver = bs->drv->protocol_name;
>>      BDRVBlkioState *s = bs->opaque;
>>      bool fd_supported = false;
>> -    int fd, ret;
>> +    int ret;
>>
>>      if (!path) {
>>          error_setg(errp, "missing 'path' option");
>> @@ -678,7 +678,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
>>      }
>>
>>      if (strcmp(blkio_driver, "virtio-blk-vhost-vdpa") == 0 &&
>> -        blkio_get_int(s->blkio, "fd", &fd) == 0) {
>> +        blkio_set_int(s->blkio, "fd", -1) == 0) {
>>          fd_supported = true;
>>      }
>>
>> @@ -688,7 +688,7 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
>>       * layer through the "/dev/fdset/N" special path.
>>       */
>>      if (fd_supported) {
>> -        int open_flags;
>> +        int open_flags, fd;
>>
>>          if (flags & BDRV_O_RDWR) {
>>              open_flags = O_RDWR;
>> --
>> 2.41.0
>>