[Qemu-devel] [PATCH 0/2] iscsi: Fix bs->request_alignment failure on LUN 0

[Qemu-devel] [PATCH 0/2] iscsi: Fix bs->request_alignment failure on LUN 0

[Kevin Wolf]

Kevin Wolf (2):
  iscsi: Use bs->sg for everything else than disks
  block: Fix bs->request_alignment assertion for bs->sg=1

 block.c       | 2 +-
 block/iscsi.c | 9 ++++-----
 2 files changed, 5 insertions(+), 6 deletions(-)

-- 
1.8.1.4

[Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than disks

[Kevin Wolf]

The current iscsi block driver code makes the rather arbitrary decision
that TYPE_MEDIUM_CHANGER and TYPE_TAPE devices have bs->sg = 1 and all
other device types are disks.

Instead of this, check for TYPE_DISK to expose the disk interface and
make everything else bs->sg = 1. In particular, this includes devices
with TYPE_STORAGE_ARRAY, which is what LUN 0 of an iscsi target is.
(See https://bugzilla.redhat.com/show_bug.cgi?id=1067784 for the exact
scenario.)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/iscsi.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index 0a15f53..b490e98 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -1231,12 +1231,11 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
     bs->total_sectors = sector_lun2qemu(iscsilun->num_blocks, iscsilun);
     bs->request_alignment = iscsilun->block_size;
 
-    /* Medium changer or tape. We dont have any emulation for this so this must
-     * be sg ioctl compatible. We force it to be sg, otherwise qemu will try
-     * to read from the device to guess the image format.
+    /* We don't have any emulation for devices other than disks and CD-ROMs, so
+     * this must be sg ioctl compatible. We force it to be sg, otherwise qemu
+     * will try to read from the device to guess the image format.
      */
-    if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
-        iscsilun->type == TYPE_TAPE) {
+    if (iscsilun->type != TYPE_DISK && iscsilun->type != TYPE_ROM) {
         bs->sg = 1;
     }
 
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than disks

[Benoît Canet]

The Wednesday 05 Mar 2014 à 16:00:48 (+0100), Kevin Wolf wrote :
> The current iscsi block driver code makes the rather arbitrary decision
> that TYPE_MEDIUM_CHANGER and TYPE_TAPE devices have bs->sg = 1 and all
> other device types are disks.
> 
> Instead of this, check for TYPE_DISK to expose the disk interface and
> make everything else bs->sg = 1. In particular, this includes devices
> with TYPE_STORAGE_ARRAY, which is what LUN 0 of an iscsi target is.
> (See https://bugzilla.redhat.com/show_bug.cgi?id=1067784 for the exact
> scenario.)
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/iscsi.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/block/iscsi.c b/block/iscsi.c
> index 0a15f53..b490e98 100644
> --- a/block/iscsi.c
> +++ b/block/iscsi.c
> @@ -1231,12 +1231,11 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
>      bs->total_sectors = sector_lun2qemu(iscsilun->num_blocks, iscsilun);
>      bs->request_alignment = iscsilun->block_size;
>  
> -    /* Medium changer or tape. We dont have any emulation for this so this must
> -     * be sg ioctl compatible. We force it to be sg, otherwise qemu will try
> -     * to read from the device to guess the image format.
> +    /* We don't have any emulation for devices other than disks and CD-ROMs, so
> +     * this must be sg ioctl compatible. We force it to be sg, otherwise qemu
> +     * will try to read from the device to guess the image format.
>       */
> -    if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
> -        iscsilun->type == TYPE_TAPE) {
> +    if (iscsilun->type != TYPE_DISK && iscsilun->type != TYPE_ROM) {
I don't understand you are talking about type TYPE_STORAGE_ARRAY in the commit
message but testing against TYPE_ROM and they are not the same.
Maybe a comment explaining the role of TYPE_ROM would give a clue to non scsi
savy persons like me.

Best regards

Benoît

>          bs->sg = 1;
>      }
>  
> -- 
> 1.8.1.4
> 
> 

Re: [Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than disks

[Kevin Wolf]

Am 05.03.2014 um 16:33 hat Benoît Canet geschrieben:
> The Wednesday 05 Mar 2014 à 16:00:48 (+0100), Kevin Wolf wrote :
> > The current iscsi block driver code makes the rather arbitrary decision
> > that TYPE_MEDIUM_CHANGER and TYPE_TAPE devices have bs->sg = 1 and all
> > other device types are disks.
> > 
> > Instead of this, check for TYPE_DISK to expose the disk interface and
> > make everything else bs->sg = 1. In particular, this includes devices
> > with TYPE_STORAGE_ARRAY, which is what LUN 0 of an iscsi target is.
> > (See https://bugzilla.redhat.com/show_bug.cgi?id=1067784 for the exact
> > scenario.)
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  block/iscsi.c | 9 ++++-----
> >  1 file changed, 4 insertions(+), 5 deletions(-)
> > 
> > diff --git a/block/iscsi.c b/block/iscsi.c
> > index 0a15f53..b490e98 100644
> > --- a/block/iscsi.c
> > +++ b/block/iscsi.c
> > @@ -1231,12 +1231,11 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
> >      bs->total_sectors = sector_lun2qemu(iscsilun->num_blocks, iscsilun);
> >      bs->request_alignment = iscsilun->block_size;
> >  
> > -    /* Medium changer or tape. We dont have any emulation for this so this must
> > -     * be sg ioctl compatible. We force it to be sg, otherwise qemu will try
> > -     * to read from the device to guess the image format.
> > +    /* We don't have any emulation for devices other than disks and CD-ROMs, so
> > +     * this must be sg ioctl compatible. We force it to be sg, otherwise qemu
> > +     * will try to read from the device to guess the image format.
> >       */
> > -    if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
> > -        iscsilun->type == TYPE_TAPE) {
> > +    if (iscsilun->type != TYPE_DISK && iscsilun->type != TYPE_ROM) {
> I don't understand you are talking about type TYPE_STORAGE_ARRAY in the commit
> message but testing against TYPE_ROM and they are not the same.
> Maybe a comment explaining the role of TYPE_ROM would give a clue to non scsi
> savy persons like me.

TYPE_STORAGE_ARRAY is what exposed the bug (see the Bugzilla reference).
It was previously bs->sg = 0, but becomes now bs->sg = 1. The reason for
this is that the usual block layer operations only work on disks (i.e.
hard disks = TYPE_DISK and CD-ROM drives = TYPE_ROM), so for all the
rest we can only expose a generic SCSI device, but no real block device.

Kevin

Re: [Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than disks

[Benoît Canet]

The Wednesday 05 Mar 2014 à 16:41:20 (+0100), Kevin Wolf wrote :
> Am 05.03.2014 um 16:33 hat Benoît Canet geschrieben:
> > The Wednesday 05 Mar 2014 à 16:00:48 (+0100), Kevin Wolf wrote :
> > > The current iscsi block driver code makes the rather arbitrary decision
> > > that TYPE_MEDIUM_CHANGER and TYPE_TAPE devices have bs->sg = 1 and all
> > > other device types are disks.
> > > 
> > > Instead of this, check for TYPE_DISK to expose the disk interface and
> > > make everything else bs->sg = 1. In particular, this includes devices
> > > with TYPE_STORAGE_ARRAY, which is what LUN 0 of an iscsi target is.
> > > (See https://bugzilla.redhat.com/show_bug.cgi?id=1067784 for the exact
> > > scenario.)
> > > 
> > > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > > ---
> > >  block/iscsi.c | 9 ++++-----
> > >  1 file changed, 4 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/block/iscsi.c b/block/iscsi.c
> > > index 0a15f53..b490e98 100644
> > > --- a/block/iscsi.c
> > > +++ b/block/iscsi.c
> > > @@ -1231,12 +1231,11 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
> > >      bs->total_sectors = sector_lun2qemu(iscsilun->num_blocks, iscsilun);
> > >      bs->request_alignment = iscsilun->block_size;
> > >  
> > > -    /* Medium changer or tape. We dont have any emulation for this so this must
> > > -     * be sg ioctl compatible. We force it to be sg, otherwise qemu will try
> > > -     * to read from the device to guess the image format.
> > > +    /* We don't have any emulation for devices other than disks and CD-ROMs, so
> > > +     * this must be sg ioctl compatible. We force it to be sg, otherwise qemu
> > > +     * will try to read from the device to guess the image format.
> > >       */
> > > -    if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
> > > -        iscsilun->type == TYPE_TAPE) {
> > > +    if (iscsilun->type != TYPE_DISK && iscsilun->type != TYPE_ROM) {
> > I don't understand you are talking about type TYPE_STORAGE_ARRAY in the commit
> > message but testing against TYPE_ROM and they are not the same.
> > Maybe a comment explaining the role of TYPE_ROM would give a clue to non scsi
> > savy persons like me.
> 
> TYPE_STORAGE_ARRAY is what exposed the bug (see the Bugzilla reference).
> It was previously bs->sg = 0, but becomes now bs->sg = 1. The reason for
> this is that the usual block layer operations only work on disks (i.e.
> hard disks = TYPE_DISK and CD-ROM drives = TYPE_ROM), so for all the
> rest we can only expose a generic SCSI device, but no real block device.

Ok I didn't knew that TYPE_ROM == type of CDROM. It's simpler now.

Reviewed-by: Benoit Canet <benoit@irqsave.net>

> 
> Kevin
> 

Re: [Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than disks

[Peter Lieven]

Am 05.03.2014 16:00, schrieb Kevin Wolf:
> The current iscsi block driver code makes the rather arbitrary decision
> that TYPE_MEDIUM_CHANGER and TYPE_TAPE devices have bs->sg = 1 and all
> other device types are disks.
>
> Instead of this, check for TYPE_DISK to expose the disk interface and
> make everything else bs->sg = 1. In particular, this includes devices
> with TYPE_STORAGE_ARRAY, which is what LUN 0 of an iscsi target is.
> (See https://bugzilla.redhat.com/show_bug.cgi?id=1067784 for the exact
> scenario.)
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/iscsi.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/block/iscsi.c b/block/iscsi.c
> index 0a15f53..b490e98 100644
> --- a/block/iscsi.c
> +++ b/block/iscsi.c
> @@ -1231,12 +1231,11 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
>      bs->total_sectors = sector_lun2qemu(iscsilun->num_blocks, iscsilun);
>      bs->request_alignment = iscsilun->block_size;
>  
> -    /* Medium changer or tape. We dont have any emulation for this so this must
> -     * be sg ioctl compatible. We force it to be sg, otherwise qemu will try
> -     * to read from the device to guess the image format.
> +    /* We don't have any emulation for devices other than disks and CD-ROMs, so
> +     * this must be sg ioctl compatible. We force it to be sg, otherwise qemu
> +     * will try to read from the device to guess the image format.
>       */
> -    if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
> -        iscsilun->type == TYPE_TAPE) {
> +    if (iscsilun->type != TYPE_DISK && iscsilun->type != TYPE_ROM) {
>          bs->sg = 1;
>      }
>  
We have ioctl support in the iscsi block driver only for Linux. Is this a problem?

Peter

Re: [Qemu-devel] [PATCH 1/2] iscsi: Use bs->sg for everything else than disks

[Kevin Wolf]

Am 05.03.2014 um 17:02 hat Peter Lieven geschrieben:
> Am 05.03.2014 16:00, schrieb Kevin Wolf:
> > The current iscsi block driver code makes the rather arbitrary decision
> > that TYPE_MEDIUM_CHANGER and TYPE_TAPE devices have bs->sg = 1 and all
> > other device types are disks.
> >
> > Instead of this, check for TYPE_DISK to expose the disk interface and
> > make everything else bs->sg = 1. In particular, this includes devices
> > with TYPE_STORAGE_ARRAY, which is what LUN 0 of an iscsi target is.
> > (See https://bugzilla.redhat.com/show_bug.cgi?id=1067784 for the exact
> > scenario.)
> >
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  block/iscsi.c | 9 ++++-----
> >  1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/block/iscsi.c b/block/iscsi.c
> > index 0a15f53..b490e98 100644
> > --- a/block/iscsi.c
> > +++ b/block/iscsi.c
> > @@ -1231,12 +1231,11 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
> >      bs->total_sectors = sector_lun2qemu(iscsilun->num_blocks, iscsilun);
> >      bs->request_alignment = iscsilun->block_size;
> >  
> > -    /* Medium changer or tape. We dont have any emulation for this so this must
> > -     * be sg ioctl compatible. We force it to be sg, otherwise qemu will try
> > -     * to read from the device to guess the image format.
> > +    /* We don't have any emulation for devices other than disks and CD-ROMs, so
> > +     * this must be sg ioctl compatible. We force it to be sg, otherwise qemu
> > +     * will try to read from the device to guess the image format.
> >       */
> > -    if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
> > -        iscsilun->type == TYPE_TAPE) {
> > +    if (iscsilun->type != TYPE_DISK && iscsilun->type != TYPE_ROM) {
> >          bs->sg = 1;
> >      }
> >  
> We have ioctl support in the iscsi block driver only for Linux. Is this a problem?

Should be okay. It will cause the requests to fail, obviously
(bdrv_ioctl returns -ENOTSUP, and bdrv_aio_ioctl returns NULL), but
callers seem to cope with it and if we don't know how to handle the
request, that's the right thing to do.

Kevin

[Qemu-devel] [PATCH 2/2] block: Fix bs->request_alignment assertion for bs->sg=1

[Kevin Wolf]

For sg backends, bs->request_alignment is meaningless and may be 0.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 38bbdf3..f01b91c 100644
--- a/block.c
+++ b/block.c
@@ -935,7 +935,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
 
     bdrv_refresh_limits(bs);
     assert(bdrv_opt_mem_align(bs) != 0);
-    assert(bs->request_alignment != 0);
+    assert((bs->request_alignment != 0) || bs->sg);
 
 #ifndef _WIN32
     if (bs->is_temporary) {
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH 2/2] block: Fix bs->request_alignment assertion for bs->sg=1

[Benoît Canet]

The Wednesday 05 Mar 2014 à 16:00:49 (+0100), Kevin Wolf wrote :
> For sg backends, bs->request_alignment is meaningless and may be 0.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block.c b/block.c
> index 38bbdf3..f01b91c 100644
> --- a/block.c
> +++ b/block.c
> @@ -935,7 +935,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
>  
>      bdrv_refresh_limits(bs);
>      assert(bdrv_opt_mem_align(bs) != 0);
> -    assert(bs->request_alignment != 0);
> +    assert((bs->request_alignment != 0) || bs->sg);
>  
>  #ifndef _WIN32
>      if (bs->is_temporary) {
> -- 
> 1.8.1.4
> 
> 
Reviewed-by: Benoit Canet <benoit@irqsave.net>

Re: [Qemu-devel] [PATCH 0/2] iscsi: Fix bs->request_alignment failure on LUN 0

[Paolo Bonzini]

Il 05/03/2014 16:00, Kevin Wolf ha scritto:
> Kevin Wolf (2):
>   iscsi: Use bs->sg for everything else than disks
>   block: Fix bs->request_alignment assertion for bs->sg=1
>
>  block.c       | 2 +-
>  block/iscsi.c | 9 ++++-----
>  2 files changed, 5 insertions(+), 6 deletions(-)
>

Looks good.  Thanks!

Paolo