| Message ID | 1446657582-21619-9-git-send-email-den@openvz.org |
|---|---|
| State | New |
| Headers | show |
On Wed, Nov 04, 2015 at 08:19:39PM +0300, Denis V. Lunev wrote: > +BlockDriverState *bdrv_all_find_vmstate_bs(void) > +{ > + BlockDriverState *bs = NULL; > + > + while ((bs = bdrv_next(bs))) { > + AioContext *ctx = bdrv_get_aio_context(bs); > + > + aio_context_acquire(ctx); > + if (bdrv_can_snapshot(bs)) { > + return bs; This leaves AioContext acquired. If that is intentional then it must be documented because it looks like a bug. Normally functions that do this have an AioContext **aio_context agument so the caller does aio_context_release() later. This way it's obvious that the caller needs to release. For example, see blockdev.c:find_block_job(). > + } > + aio_context_release(ctx); > + } > + return NULL; > +} > + > +void bdrv_unlock(BlockDriverState *bs) > +{ > + aio_context_release(bdrv_get_aio_context(bs)); > +} This API is weird. There is no lock function. Please do what I mentioned above. Another advantage of that approach is that we are 100% sure to release the same AioContext that was acquired (even if bdrv_set_aio_context() gets called halfway through).
On 11/06/2015 06:18 PM, Stefan Hajnoczi wrote: > On Wed, Nov 04, 2015 at 08:19:39PM +0300, Denis V. Lunev wrote: >> +BlockDriverState *bdrv_all_find_vmstate_bs(void) >> +{ >> + BlockDriverState *bs = NULL; >> + >> + while ((bs = bdrv_next(bs))) { >> + AioContext *ctx = bdrv_get_aio_context(bs); >> + >> + aio_context_acquire(ctx); >> + if (bdrv_can_snapshot(bs)) { >> + return bs; > This leaves AioContext acquired. If that is intentional then it must be > documented because it looks like a bug. > > Normally functions that do this have an AioContext **aio_context agument > so the caller does aio_context_release() later. This way it's obvious > that the caller needs to release. > > For example, see blockdev.c:find_block_job(). > >> + } >> + aio_context_release(ctx); >> + } >> + return NULL; >> +} >> + >> +void bdrv_unlock(BlockDriverState *bs) >> +{ >> + aio_context_release(bdrv_get_aio_context(bs)); >> +} > This API is weird. There is no lock function. Please do what I > mentioned above. > > Another advantage of that approach is that we are 100% sure to release > the same AioContext that was acquired (even if bdrv_set_aio_context() > gets called halfway through). no prob if Juan will accept that :) Ho does not want to care and take the lock anywhere in his code. For me this is pure matter of taste.
diff --git a/block/snapshot.c b/block/snapshot.c index bb3bfd5..e196c9b 100644 --- a/block/snapshot.c +++ b/block/snapshot.c @@ -446,3 +446,24 @@ int bdrv_all_find_snapshot(const char *name, BlockDriverState **first_bad_bs) *first_bad_bs = bs; return err; } + +BlockDriverState *bdrv_all_find_vmstate_bs(void) +{ + BlockDriverState *bs = NULL; + + while ((bs = bdrv_next(bs))) { + AioContext *ctx = bdrv_get_aio_context(bs); + + aio_context_acquire(ctx); + if (bdrv_can_snapshot(bs)) { + return bs; + } + aio_context_release(ctx); + } + return NULL; +} + +void bdrv_unlock(BlockDriverState *bs) +{ + aio_context_release(bdrv_get_aio_context(bs)); +} diff --git a/include/block/snapshot.h b/include/block/snapshot.h index 44c3a38..1f45f51 100644 --- a/include/block/snapshot.h +++ b/include/block/snapshot.h @@ -88,4 +88,7 @@ int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bsd_bs, int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bsd_bs); int bdrv_all_find_snapshot(const char *name, BlockDriverState **first_bad_bs); +BlockDriverState *bdrv_all_find_vmstate_bs(void); +void bdrv_unlock(BlockDriverState *bs); + #endif diff --git a/migration/savevm.c b/migration/savevm.c index dbcb313..9339f2e 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -1237,17 +1237,6 @@ out: return ret; } -static BlockDriverState *find_vmstate_bs(void) -{ - BlockDriverState *bs = NULL; - while ((bs = bdrv_next(bs))) { - if (bdrv_can_snapshot(bs)) { - return bs; - } - } - return NULL; -} - void hmp_savevm(Monitor *mon, const QDict *qdict) { BlockDriverState *bs, *bs1; @@ -1293,8 +1282,8 @@ void hmp_savevm(Monitor *mon, const QDict *qdict) sn->date_nsec = tv.tv_usec * 1000; sn->vm_clock_nsec = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); - bs = find_vmstate_bs(); - if (!bs) { + bs = bdrv_all_find_vmstate_bs(); + if (bs == NULL) { monitor_printf(mon, "No block device can accept snapshots\n"); goto the_end; } @@ -1312,6 +1301,7 @@ void hmp_savevm(Monitor *mon, const QDict *qdict) localtime_r((const time_t *)&tv.tv_sec, &tm); strftime(sn->name, sizeof(sn->name), "vm-%Y%m%d%H%M%S", &tm); } + bdrv_unlock(bs); /* save the VM state */ f = qemu_fopen_bdrv(bs, 1); @@ -1395,7 +1385,7 @@ int load_vmstate(const char *name) return ret; } - bs_vm_state = find_vmstate_bs(); + bs_vm_state = bdrv_all_find_vmstate_bs(); if (!bs_vm_state) { error_report("No block device supports snapshots"); return -ENOTSUP; @@ -1403,6 +1393,8 @@ int load_vmstate(const char *name) /* Don't even try to load empty VM states */ ret = bdrv_snapshot_find(bs_vm_state, &sn, name); + bdrv_unlock(bs_vm_state); + if (ret < 0) { return ret; } else if (sn.vm_state_size == 0) { @@ -1464,13 +1456,14 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict) int total; int *available_snapshots; - bs = find_vmstate_bs(); + bs = bdrv_all_find_vmstate_bs(); if (!bs) { monitor_printf(mon, "No available block device supports snapshots\n"); return; } nb_sns = bdrv_snapshot_list(bs, &sn_tab); + bdrv_unlock(bs); if (nb_sns < 0) { monitor_printf(mon, "bdrv_snapshot_list: error %d\n", nb_sns); return;
bdrv_all_find_vmstate_bs will return locked BlockDriverState. The code written in the way to avoid nested locking taking into account that patch for locking inside qemu_fopen_bdrv/qemu_fclose is acceptable. Signed-off-by: Denis V. Lunev <den@openvz.org> CC: Juan Quintela <quintela@redhat.com> CC: Stefan Hajnoczi <stefanha@redhat.com> CC: Kevin Wolf <kwolf@redhat.com> --- block/snapshot.c | 21 +++++++++++++++++++++ include/block/snapshot.h | 3 +++ migration/savevm.c | 23 ++++++++--------------- 3 files changed, 32 insertions(+), 15 deletions(-)