| Message ID | 1472767012-7641-2-git-send-email-jsnow@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 09/01/2016 04:56 PM, John Snow wrote: > If a device still has an attached BDS because the medium has not yet > been removed, we will be unable to migrate to a new host because > blk_flush will return an error for that backend. > > Replace the call to blk_is_available to blk_is_inserted to weaken > the check and allow flushes from the backend to work, while still > disallowing flushes from the frontend/device model to work. Sounds slightly nicer if you stop short: s/ to work// > > This fixes a regression present in 2.6.0 caused by the following commit: > fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf > block: Move some bdrv_*_all() functions to BB > > Signed-off-by: John Snow <jsnow@redhat.com> > --- > block/block-backend.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) Reviewed-by: Eric Blake <eblake@redhat.com> However, I don't have an offhand suggestion on how best to test it.
On 09/01/2016 06:11 PM, Eric Blake wrote:
> Sounds slightly nicer if you stop short: s/ to work//
I'm happy with this edit if a maintainer would like to make it.
On Thu, Sep 01, 2016 at 05:56:52PM -0400, John Snow wrote: > If a device still has an attached BDS because the medium has not yet > been removed, we will be unable to migrate to a new host because > blk_flush will return an error for that backend. > > Replace the call to blk_is_available to blk_is_inserted to weaken > the check and allow flushes from the backend to work, while still > disallowing flushes from the frontend/device model to work. > > This fixes a regression present in 2.6.0 caused by the following commit: > fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf > block: Move some bdrv_*_all() functions to BB > > Signed-off-by: John Snow <jsnow@redhat.com> Reviewed-by: Jeff Cody <jcody@redhat.com> I don't have any real suggestions for a test either, except to point you to test 091 which does a live migration test (which is not very helpful, I know). > --- > block/block-backend.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/block/block-backend.c b/block/block-backend.c > index effa038..36a32c3 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c > @@ -1058,7 +1058,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset, > BlockAIOCB *blk_aio_flush(BlockBackend *blk, > BlockCompletionFunc *cb, void *opaque) > { > - if (!blk_is_available(blk)) { > + if (!blk_is_inserted(blk)) { > return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM); > } > > @@ -1118,7 +1118,7 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int count) > > int blk_co_flush(BlockBackend *blk) > { > - if (!blk_is_available(blk)) { > + if (!blk_is_inserted(blk)) { > return -ENOMEDIUM; > } > > @@ -1127,7 +1127,7 @@ int blk_co_flush(BlockBackend *blk) > > int blk_flush(BlockBackend *blk) > { > - if (!blk_is_available(blk)) { > + if (!blk_is_inserted(blk)) { > return -ENOMEDIUM; > } > > -- > 2.7.4 > >
John Snow <jsnow@redhat.com> writes: > If a device still has an attached BDS because the medium has not yet > been removed, we will be unable to migrate to a new host because > blk_flush will return an error for that backend. > > Replace the call to blk_is_available to blk_is_inserted to weaken > the check and allow flushes from the backend to work, while still > disallowing flushes from the frontend/device model to work. > > This fixes a regression present in 2.6.0 caused by the following commit: > fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf > block: Move some bdrv_*_all() functions to BB > > Signed-off-by: John Snow <jsnow@redhat.com> > --- > block/block-backend.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/block/block-backend.c b/block/block-backend.c > index effa038..36a32c3 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c > @@ -1058,7 +1058,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset, > BlockAIOCB *blk_aio_flush(BlockBackend *blk, > BlockCompletionFunc *cb, void *opaque) > { > - if (!blk_is_available(blk)) { > + if (!blk_is_inserted(blk)) { > return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM); > } > > @@ -1118,7 +1118,7 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int count) > > int blk_co_flush(BlockBackend *blk) > { > - if (!blk_is_available(blk)) { > + if (!blk_is_inserted(blk)) { > return -ENOMEDIUM; > } > > @@ -1127,7 +1127,7 @@ int blk_co_flush(BlockBackend *blk) > > int blk_flush(BlockBackend *blk) > { > - if (!blk_is_available(blk)) { > + if (!blk_is_inserted(blk)) { > return -ENOMEDIUM; > } Naive question: should we flush before we open the tray?
On 09/02/2016 01:44 AM, Markus Armbruster wrote: > John Snow <jsnow@redhat.com> writes: > >> If a device still has an attached BDS because the medium has not yet >> been removed, we will be unable to migrate to a new host because >> blk_flush will return an error for that backend. >> >> Replace the call to blk_is_available to blk_is_inserted to weaken >> the check and allow flushes from the backend to work, while still >> disallowing flushes from the frontend/device model to work. >> >> This fixes a regression present in 2.6.0 caused by the following commit: >> fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf >> block: Move some bdrv_*_all() functions to BB >> >> Signed-off-by: John Snow <jsnow@redhat.com> >> --- >> block/block-backend.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/block/block-backend.c b/block/block-backend.c >> index effa038..36a32c3 100644 >> --- a/block/block-backend.c >> +++ b/block/block-backend.c >> @@ -1058,7 +1058,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset, >> BlockAIOCB *blk_aio_flush(BlockBackend *blk, >> BlockCompletionFunc *cb, void *opaque) >> { >> - if (!blk_is_available(blk)) { >> + if (!blk_is_inserted(blk)) { >> return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM); >> } >> >> @@ -1118,7 +1118,7 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int count) >> >> int blk_co_flush(BlockBackend *blk) >> { >> - if (!blk_is_available(blk)) { >> + if (!blk_is_inserted(blk)) { >> return -ENOMEDIUM; >> } >> >> @@ -1127,7 +1127,7 @@ int blk_co_flush(BlockBackend *blk) >> >> int blk_flush(BlockBackend *blk) >> { >> - if (!blk_is_available(blk)) { >> + if (!blk_is_inserted(blk)) { >> return -ENOMEDIUM; >> } > > Naive question: should we flush before we open the tray? > Naive, but long-winded answer: There are two types of flushes to me, conceptually: Frontend and Backend. Frontend would be a request from the quest to flush. If the medium in question is absent, this should rightly fail. I do expect this to be handled at the device layer. Backend is a request from QEMU for various reasons, like needing to drain the queue for migration or savevm. What's happening here is that we have a backend request to flush a medium that is inaccessible to the guest -- The flush all routine is ignorant of this fact. So we get a migration request with an open tray (because the user had opened it some time prior perhaps, and left it open unwittingly) and it fails because its inaccessible to the guest. Migration fails as a result. That seems wrong to me. A few ways to fix it: (1) Have internal flush requests be aware of the fact that there's nothing to flush here: this is a read-only media and we could skip it. (2) Allow flush to fail in a non-fatal way for cases where we need to flush, but cannot (-ENOMEDIUM) and where it would rightly fail on a real machine. (3) Just allow flushes to work on devices not visible to the guest, which is what I've done here. Internal requests should work, Guest requests should fail. I was briefly concerned about "What if this lets us flush something we shouldn't?" and Max's take was "That doesn't seem so bad. CDROMs are RO anyway." So I went with the easiest option here. To answer your question more directly, we aren't choosing to eject-then-flush, the user is. I can't move the flush before the eject unless we flush-on-eject internally, then mark the device explicitly as not needing to be flushed anymore, but that's essentially (1) up there. --js
John Snow <jsnow@redhat.com> writes: > On 09/02/2016 01:44 AM, Markus Armbruster wrote: >> John Snow <jsnow@redhat.com> writes: >> >>> If a device still has an attached BDS because the medium has not yet >>> been removed, we will be unable to migrate to a new host because >>> blk_flush will return an error for that backend. >>> >>> Replace the call to blk_is_available to blk_is_inserted to weaken >>> the check and allow flushes from the backend to work, while still >>> disallowing flushes from the frontend/device model to work. >>> >>> This fixes a regression present in 2.6.0 caused by the following commit: >>> fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf >>> block: Move some bdrv_*_all() functions to BB >>> >>> Signed-off-by: John Snow <jsnow@redhat.com> >>> --- >>> block/block-backend.c | 6 +++--- >>> 1 file changed, 3 insertions(+), 3 deletions(-) >>> >>> diff --git a/block/block-backend.c b/block/block-backend.c >>> index effa038..36a32c3 100644 >>> --- a/block/block-backend.c >>> +++ b/block/block-backend.c >>> @@ -1058,7 +1058,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset, >>> BlockAIOCB *blk_aio_flush(BlockBackend *blk, >>> BlockCompletionFunc *cb, void *opaque) >>> { >>> - if (!blk_is_available(blk)) { >>> + if (!blk_is_inserted(blk)) { >>> return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM); >>> } >>> >>> @@ -1118,7 +1118,7 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int count) >>> >>> int blk_co_flush(BlockBackend *blk) >>> { >>> - if (!blk_is_available(blk)) { >>> + if (!blk_is_inserted(blk)) { >>> return -ENOMEDIUM; >>> } >>> >>> @@ -1127,7 +1127,7 @@ int blk_co_flush(BlockBackend *blk) >>> >>> int blk_flush(BlockBackend *blk) >>> { >>> - if (!blk_is_available(blk)) { >>> + if (!blk_is_inserted(blk)) { >>> return -ENOMEDIUM; >>> } >> >> Naive question: should we flush before we open the tray? >> > > Naive, but long-winded answer: > > There are two types of flushes to me, conceptually: > > Frontend and Backend. > > Frontend would be a request from the quest to flush. If the medium in > question is absent, this should rightly fail. I do expect this to be > handled at the device layer. > > Backend is a request from QEMU for various reasons, like needing to > drain the queue for migration or savevm. > > What's happening here is that we have a backend request to flush a > medium that is inaccessible to the guest Assuming we caught frontend requests at the device layer already. > -- The flush all routine is > ignorant of this fact. So we get a migration request with an open tray > (because the user had opened it some time prior perhaps, and left it > open unwittingly) and it fails because its inaccessible to the > guest. Migration fails as a result. > > That seems wrong to me. A few ways to fix it: > > (1) Have internal flush requests be aware of the fact that there's > nothing to flush here: this is a read-only media and we could skip it. Returning successfully because there's nothing to flush makes sense to me. > (2) Allow flush to fail in a non-fatal way for cases where we need to > flush, but cannot (-ENOMEDIUM) and where it would rightly fail on a > real machine. I don't like -ENOMEDIUM when there's nothing to flush. > (3) Just allow flushes to work on devices not visible to the guest, > which is what I've done here. Internal requests should work, Guest > requests should fail. I guess that's okay, ... > I was briefly concerned about "What if this lets us flush something we > shouldn't?" and Max's take was "That doesn't seem so bad. CDROMs are > RO anyway." ... even though I don't buy Max's reason. Writable removable media exist. The argument I can buy is that internal requests are fundamentally different from external requests. > So I went with the easiest option here. > > To answer your question more directly, we aren't choosing to > eject-then-flush, the user is. I can't move the flush before the eject > unless we flush-on-eject internally, then mark the device explicitly > as not needing to be flushed anymore, but that's essentially (1) up > there. > > --js
On 09/05/2016 05:15 AM, Markus Armbruster wrote: > John Snow <jsnow@redhat.com> writes: > >> On 09/02/2016 01:44 AM, Markus Armbruster wrote: >>> John Snow <jsnow@redhat.com> writes: >>> >>>> If a device still has an attached BDS because the medium has not yet >>>> been removed, we will be unable to migrate to a new host because >>>> blk_flush will return an error for that backend. >>>> >>>> Replace the call to blk_is_available to blk_is_inserted to weaken >>>> the check and allow flushes from the backend to work, while still >>>> disallowing flushes from the frontend/device model to work. >>>> >>>> This fixes a regression present in 2.6.0 caused by the following commit: >>>> fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf >>>> block: Move some bdrv_*_all() functions to BB >>>> >>>> Signed-off-by: John Snow <jsnow@redhat.com> >>>> --- >>>> block/block-backend.c | 6 +++--- >>>> 1 file changed, 3 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/block/block-backend.c b/block/block-backend.c >>>> index effa038..36a32c3 100644 >>>> --- a/block/block-backend.c >>>> +++ b/block/block-backend.c >>>> @@ -1058,7 +1058,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset, >>>> BlockAIOCB *blk_aio_flush(BlockBackend *blk, >>>> BlockCompletionFunc *cb, void *opaque) >>>> { >>>> - if (!blk_is_available(blk)) { >>>> + if (!blk_is_inserted(blk)) { >>>> return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM); >>>> } >>>> >>>> @@ -1118,7 +1118,7 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int count) >>>> >>>> int blk_co_flush(BlockBackend *blk) >>>> { >>>> - if (!blk_is_available(blk)) { >>>> + if (!blk_is_inserted(blk)) { >>>> return -ENOMEDIUM; >>>> } >>>> >>>> @@ -1127,7 +1127,7 @@ int blk_co_flush(BlockBackend *blk) >>>> >>>> int blk_flush(BlockBackend *blk) >>>> { >>>> - if (!blk_is_available(blk)) { >>>> + if (!blk_is_inserted(blk)) { >>>> return -ENOMEDIUM; >>>> } >>> >>> Naive question: should we flush before we open the tray? >>> >> >> Naive, but long-winded answer: >> >> There are two types of flushes to me, conceptually: >> >> Frontend and Backend. >> >> Frontend would be a request from the quest to flush. If the medium in >> question is absent, this should rightly fail. I do expect this to be >> handled at the device layer. >> >> Backend is a request from QEMU for various reasons, like needing to >> drain the queue for migration or savevm. >> >> What's happening here is that we have a backend request to flush a >> medium that is inaccessible to the guest > > Assuming we caught frontend requests at the device layer already. > >> -- The flush all routine is >> ignorant of this fact. So we get a migration request with an open tray >> (because the user had opened it some time prior perhaps, and left it >> open unwittingly) and it fails because its inaccessible to the >> guest. Migration fails as a result. >> >> That seems wrong to me. A few ways to fix it: >> >> (1) Have internal flush requests be aware of the fact that there's >> nothing to flush here: this is a read-only media and we could skip it. > > Returning successfully because there's nothing to flush makes sense to > me. > Only slightly more involved. At the time I wrote the first patch, I don't think Denis' improvements had gone in yet, and I still haven't really looked at them to see how easy they are to co-opt here. >> (2) Allow flush to fail in a non-fatal way for cases where we need to >> flush, but cannot (-ENOMEDIUM) and where it would rightly fail on a >> real machine. > > I don't like -ENOMEDIUM when there's nothing to flush. > >> (3) Just allow flushes to work on devices not visible to the guest, >> which is what I've done here. Internal requests should work, Guest >> requests should fail. > > I guess that's okay, ... > Conceptually, QEMU should be allowed to flush things to its internal drive abstractions regardless of what it looks like to the guest whenever it decides it is necessary to. In practice, I don't know how clean we are about separating out who is requesting the flush to know which to deny. >> I was briefly concerned about "What if this lets us flush something we >> shouldn't?" and Max's take was "That doesn't seem so bad. CDROMs are >> RO anyway." > > ... even though I don't buy Max's reason. Writable removable media > exist. The argument I can buy is that internal requests are > fundamentally different from external requests. > Yeah, I think any such flush request should be denied by the device model. >> So I went with the easiest option here. >> >> To answer your question more directly, we aren't choosing to >> eject-then-flush, the user is. I can't move the flush before the eject >> unless we flush-on-eject internally, then mark the device explicitly >> as not needing to be flushed anymore, but that's essentially (1) up >> there. >> >> --js I am at the moment inclined to stick with the existing solution "for now" and add hardening against flush requests from the guest later within the 2.8 window if needed. --js
John Snow <jsnow@redhat.com> writes: > On 09/05/2016 05:15 AM, Markus Armbruster wrote: >> John Snow <jsnow@redhat.com> writes: >> >>> On 09/02/2016 01:44 AM, Markus Armbruster wrote: >>>> John Snow <jsnow@redhat.com> writes: >>>> >>>>> If a device still has an attached BDS because the medium has not yet >>>>> been removed, we will be unable to migrate to a new host because >>>>> blk_flush will return an error for that backend. >>>>> >>>>> Replace the call to blk_is_available to blk_is_inserted to weaken >>>>> the check and allow flushes from the backend to work, while still >>>>> disallowing flushes from the frontend/device model to work. >>>>> >>>>> This fixes a regression present in 2.6.0 caused by the following commit: >>>>> fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf >>>>> block: Move some bdrv_*_all() functions to BB >>>>> >>>>> Signed-off-by: John Snow <jsnow@redhat.com> >>>>> --- >>>>> block/block-backend.c | 6 +++--- >>>>> 1 file changed, 3 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/block/block-backend.c b/block/block-backend.c >>>>> index effa038..36a32c3 100644 >>>>> --- a/block/block-backend.c >>>>> +++ b/block/block-backend.c >>>>> @@ -1058,7 +1058,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset, >>>>> BlockAIOCB *blk_aio_flush(BlockBackend *blk, >>>>> BlockCompletionFunc *cb, void *opaque) >>>>> { >>>>> - if (!blk_is_available(blk)) { >>>>> + if (!blk_is_inserted(blk)) { >>>>> return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM); >>>>> } >>>>> >>>>> @@ -1118,7 +1118,7 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int count) >>>>> >>>>> int blk_co_flush(BlockBackend *blk) >>>>> { >>>>> - if (!blk_is_available(blk)) { >>>>> + if (!blk_is_inserted(blk)) { >>>>> return -ENOMEDIUM; >>>>> } >>>>> >>>>> @@ -1127,7 +1127,7 @@ int blk_co_flush(BlockBackend *blk) >>>>> >>>>> int blk_flush(BlockBackend *blk) >>>>> { >>>>> - if (!blk_is_available(blk)) { >>>>> + if (!blk_is_inserted(blk)) { >>>>> return -ENOMEDIUM; >>>>> } >>>> >>>> Naive question: should we flush before we open the tray? >>>> >>> >>> Naive, but long-winded answer: >>> >>> There are two types of flushes to me, conceptually: >>> >>> Frontend and Backend. >>> >>> Frontend would be a request from the quest to flush. If the medium in >>> question is absent, this should rightly fail. I do expect this to be >>> handled at the device layer. >>> >>> Backend is a request from QEMU for various reasons, like needing to >>> drain the queue for migration or savevm. >>> >>> What's happening here is that we have a backend request to flush a >>> medium that is inaccessible to the guest >> >> Assuming we caught frontend requests at the device layer already. >> >>> -- The flush all routine is >>> ignorant of this fact. So we get a migration request with an open tray >>> (because the user had opened it some time prior perhaps, and left it >>> open unwittingly) and it fails because its inaccessible to the >>> guest. Migration fails as a result. >>> >>> That seems wrong to me. A few ways to fix it: >>> >>> (1) Have internal flush requests be aware of the fact that there's >>> nothing to flush here: this is a read-only media and we could skip it. >> >> Returning successfully because there's nothing to flush makes sense to >> me. >> > > Only slightly more involved. At the time I wrote the first patch, I > don't think Denis' improvements had gone in yet, and I still haven't > really looked at them to see how easy they are to co-opt here. > >>> (2) Allow flush to fail in a non-fatal way for cases where we need to >>> flush, but cannot (-ENOMEDIUM) and where it would rightly fail on a >>> real machine. >> >> I don't like -ENOMEDIUM when there's nothing to flush. >> >>> (3) Just allow flushes to work on devices not visible to the guest, >>> which is what I've done here. Internal requests should work, Guest >>> requests should fail. >> >> I guess that's okay, ... >> > > Conceptually, QEMU should be allowed to flush things to its internal > drive abstractions regardless of what it looks like to the guest > whenever it decides it is necessary to. > > In practice, I don't know how clean we are about separating out who is > requesting the flush to know which to deny. Exactly. >>> I was briefly concerned about "What if this lets us flush something we >>> shouldn't?" and Max's take was "That doesn't seem so bad. CDROMs are >>> RO anyway." >> >> ... even though I don't buy Max's reason. Writable removable media >> exist. The argument I can buy is that internal requests are >> fundamentally different from external requests. >> > > Yeah, I think any such flush request should be denied by the device model. > >>> So I went with the easiest option here. >>> >>> To answer your question more directly, we aren't choosing to >>> eject-then-flush, the user is. I can't move the flush before the eject >>> unless we flush-on-eject internally, then mark the device explicitly >>> as not needing to be flushed anymore, but that's essentially (1) up >>> there. >>> >>> --js > > I am at the moment inclined to stick with the existing solution "for > now" and add hardening against flush requests from the guest later > within the 2.8 window if needed. Okay.
Am 06.09.2016 um 23:44 hat John Snow geschrieben: > On 09/05/2016 05:15 AM, Markus Armbruster wrote: > >John Snow <jsnow@redhat.com> writes: > >>(3) Just allow flushes to work on devices not visible to the guest, > >>which is what I've done here. Internal requests should work, Guest > >>requests should fail. > > > >I guess that's okay, ... > > > > Conceptually, QEMU should be allowed to flush things to its internal > drive abstractions regardless of what it looks like to the guest > whenever it decides it is necessary to. > > In practice, I don't know how clean we are about separating out who > is requesting the flush to know which to deny. Maybe the move from bdrv_flush_all() to blk_flush_all() was wrong. If you have a BDS that isn't currently attached to a guest device or at least not accessible from the guest device's BB because of things like an open tray, but the BDS has previously been written to, you still want to flush it for migration. The only other clean option I see is that we flush BDSes when they are detached from the BB, or otherwise become unaccessible (e.g. the tray is opened). And that second part suggests that it might be too easy to get this one wrong, so maybe bdrv_flush_all() was the best option after all. Kevin
diff --git a/block/block-backend.c b/block/block-backend.c index effa038..36a32c3 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -1058,7 +1058,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset, BlockAIOCB *blk_aio_flush(BlockBackend *blk, BlockCompletionFunc *cb, void *opaque) { - if (!blk_is_available(blk)) { + if (!blk_is_inserted(blk)) { return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM); } @@ -1118,7 +1118,7 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int count) int blk_co_flush(BlockBackend *blk) { - if (!blk_is_available(blk)) { + if (!blk_is_inserted(blk)) { return -ENOMEDIUM; } @@ -1127,7 +1127,7 @@ int blk_co_flush(BlockBackend *blk) int blk_flush(BlockBackend *blk) { - if (!blk_is_available(blk)) { + if (!blk_is_inserted(blk)) { return -ENOMEDIUM; }
If a device still has an attached BDS because the medium has not yet been removed, we will be unable to migrate to a new host because blk_flush will return an error for that backend. Replace the call to blk_is_available to blk_is_inserted to weaken the check and allow flushes from the backend to work, while still disallowing flushes from the frontend/device model to work. This fixes a regression present in 2.6.0 caused by the following commit: fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf block: Move some bdrv_*_all() functions to BB Signed-off-by: John Snow <jsnow@redhat.com> --- block/block-backend.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)