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[0/3] block/ssh: Add basic .bdrv_truncate()

Message ID 20180214204915.7980-1-mreitz@redhat.com
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Series block/ssh: Add basic .bdrv_truncate() | expand

Message

Max Reitz Feb. 14, 2018, 8:49 p.m. UTC 
For (x-)blockdev-create, all protocol drivers that support image
creation also need to offer a .bdrv_truncate() implementation that
matches in features.  A previous series of mine brought gluster's and
sheepdog's implementation up to par regarding preallocated truncation;
but I forgot about drivers that have a .bdrv_create() but no
.bdrv_truncate() at all.

There is only one of these, and that is ssh.  Since libssh2 does not
seem to know any way of truncating files, we can only support growing
files -- but that is what we need for (x-)blockdev-create.

Note that there are also drivers which do not support growing files,
namely iscsi and file-posix for host devices (maybe more?  I hope not).
But these also pretty much ignore the specified size on .bdrv_create()
and just use the size of the existing device.  They just check that the
specified size does not exceed the actual size, so that pretty much
matches what their .bdrv_truncate() supports, and we should be fine
there.


Max Reitz (3):
  block/ssh: Pull ssh_grow_file() from ssh_create()
  block/ssh: Make ssh_grow_file() blocking
  block/ssh: Add basic .bdrv_truncate()

 block/ssh.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 53 insertions(+), 8 deletions(-)

Comments

Max Reitz Feb. 23, 2018, 1:51 p.m. UTC | #1 
On 2018-02-14 21:49, Max Reitz wrote:
> For (x-)blockdev-create, all protocol drivers that support image
> creation also need to offer a .bdrv_truncate() implementation that
> matches in features.  A previous series of mine brought gluster's and
> sheepdog's implementation up to par regarding preallocated truncation;
> but I forgot about drivers that have a .bdrv_create() but no
> .bdrv_truncate() at all.
> 
> There is only one of these, and that is ssh.  Since libssh2 does not
> seem to know any way of truncating files, we can only support growing
> files -- but that is what we need for (x-)blockdev-create.
> 
> Note that there are also drivers which do not support growing files,
> namely iscsi and file-posix for host devices (maybe more?  I hope not).
> But these also pretty much ignore the specified size on .bdrv_create()
> and just use the size of the existing device.  They just check that the
> specified size does not exceed the actual size, so that pretty much
> matches what their .bdrv_truncate() supports, and we should be fine
> there.
> 
> 
> Max Reitz (3):
>   block/ssh: Pull ssh_grow_file() from ssh_create()
>   block/ssh: Make ssh_grow_file() blocking
>   block/ssh: Add basic .bdrv_truncate()
> 
>  block/ssh.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 53 insertions(+), 8 deletions(-)

Applied to my block branch.

Max