| Message ID | 20161203181914.7467-1-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 03.12.2016 19:19, Eric Blake wrote: > Passing a byte offset, but sector count, when we ultimately > want to operate on cluster granularity, is madness. Clean up > the interfaces to take byte offset and count. Rename > qcow2_discard_clusters() and qcow2_zero_clusters() to the > shorter qcow2_discard() and qcow2_zero() to make sure backports > don't get confused by changed units. > > Signed-off-by: Eric Blake <eblake@redhat.com> > --- > > 2.9 material, depends on 'Don't strand clusters near 2G intervals > during commit' > > block/qcow2.h | 8 ++++---- > block/qcow2-cluster.c | 20 +++++++++++--------- > block/qcow2-snapshot.c | 7 +++---- > block/qcow2.c | 22 ++++++++++------------ > 4 files changed, 28 insertions(+), 29 deletions(-) > > diff --git a/block/qcow2.h b/block/qcow2.h > index 1823414..a0d169b 100644 > --- a/block/qcow2.h > +++ b/block/qcow2.h > @@ -543,10 +543,10 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs, > int compressed_size); > > int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m); > -int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset, > - int nb_sectors, enum qcow2_discard_type type, bool full_discard); > -int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors, > - int flags); > +int qcow2_discard(BlockDriverState *bs, uint64_t offset, uint64_t count, > + enum qcow2_discard_type type, bool full_discard); > +int qcow2_zero(BlockDriverState *bs, uint64_t offset, uint64_t count, > + int flags); > > int qcow2_expand_zero_clusters(BlockDriverState *bs, > BlockDriverAmendStatusCB *status_cb, > diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c > index 928c1e2..3ee0815 100644 > --- a/block/qcow2-cluster.c > +++ b/block/qcow2-cluster.c > @@ -1511,19 +1511,17 @@ static int discard_single_l2(BlockDriverState *bs, uint64_t offset, > return nb_clusters; > } > > -int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset, > - int nb_sectors, enum qcow2_discard_type type, bool full_discard) > +int qcow2_discard(BlockDriverState *bs, uint64_t offset, uint64_t count, > + enum qcow2_discard_type type, bool full_discard) > { > BDRVQcow2State *s = bs->opaque; > uint64_t end_offset; > uint64_t nb_clusters; > int ret; > > - end_offset = offset + (nb_sectors << BDRV_SECTOR_BITS); > - > - /* Round start up and end down */ > + /* Round start up and end down to cluster boundary */ > + end_offset = start_of_cluster(s, offset + count); > offset = align_offset(offset, s->cluster_size); > - end_offset = start_of_cluster(s, end_offset); > > if (offset > end_offset) { > return 0; > @@ -1595,20 +1593,24 @@ static int zero_single_l2(BlockDriverState *bs, uint64_t offset, > return nb_clusters; > } > > -int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors, > - int flags) > +int qcow2_zero(BlockDriverState *bs, uint64_t offset, uint64_t count, > + int flags) Hmm, I personally liked qcow2_zero_clusters() better. qcow2_zero() doesn't really express that it means the verb "to zero". Also, while you are making a good point why the function should be renamed, qcow2_zero_clusters() was much more accurate because offset and count are expected to be cluster-aligned. The only alternative I can come up with would be "qcow2_write_zeroes"; that at least solves the first issue I have with this, but not the second one... > { > BDRVQcow2State *s = bs->opaque; > uint64_t nb_clusters; > int ret; > > + /* Block layer guarantees cluster alignment */ Hm, it's rather qcow2_co_pwrite_zeroes(), isn't it? The block layer will split unaligned requests into head, body and tail and it will still submit head and tail (though separately). As far as I can see, it's qcow2_co_pwrite_zeroes() which then guarantees that only the aligned part gets through to qcow2_zero(). The patch looks good apart from these nit picks, though. Max > + assert(QEMU_IS_ALIGNED(offset, s->cluster_size)); > + assert(QEMU_IS_ALIGNED(count, s->cluster_size)); > + > /* The zero flag is only supported by version 3 and newer */ > if (s->qcow_version < 3) { > return -ENOTSUP; > } > > /* Each L2 table is handled by its own loop iteration */ > - nb_clusters = size_to_clusters(s, nb_sectors << BDRV_SECTOR_BITS); > + nb_clusters = size_to_clusters(s, count); > > s->cache_discards = true;
On 12/06/2016 03:01 PM, Max Reitz wrote: > On 03.12.2016 19:19, Eric Blake wrote: >> Passing a byte offset, but sector count, when we ultimately >> want to operate on cluster granularity, is madness. Clean up >> the interfaces to take byte offset and count. Rename >> qcow2_discard_clusters() and qcow2_zero_clusters() to the >> shorter qcow2_discard() and qcow2_zero() to make sure backports >> don't get confused by changed units. >> >> Signed-off-by: Eric Blake <eblake@redhat.com> >> --- >> >> 2.9 material, depends on 'Don't strand clusters near 2G intervals >> during commit' >> >> @@ -1595,20 +1593,24 @@ static int zero_single_l2(BlockDriverState *bs, uint64_t offset, >> return nb_clusters; >> } >> >> -int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors, >> - int flags) >> +int qcow2_zero(BlockDriverState *bs, uint64_t offset, uint64_t count, >> + int flags) > > Hmm, I personally liked qcow2_zero_clusters() better. qcow2_zero() > doesn't really express that it means the verb "to zero". > > Also, while you are making a good point why the function should be > renamed, qcow2_zero_clusters() was much more accurate because offset and > count are expected to be cluster-aligned. > > The only alternative I can come up with would be "qcow2_write_zeroes"; > that at least solves the first issue I have with this, but not the > second one... Maybe qcow2_cluster_zeroize() and qcow2_cluster_discard()? That gets the benefit of the rename (to force all callers to use the right semantics), while still being legible as an object-verb naming: the action ('discard' or 'zeroize') is performed on 'qcow2 cluster' objects. > >> { >> BDRVQcow2State *s = bs->opaque; >> uint64_t nb_clusters; >> int ret; >> >> + /* Block layer guarantees cluster alignment */ > > Hm, it's rather qcow2_co_pwrite_zeroes(), isn't it? The block layer will > split unaligned requests into head, body and tail and it will still > submit head and tail (though separately). Hmm, good point. I'll have to come up with some way to reword that. > > As far as I can see, it's qcow2_co_pwrite_zeroes() which then guarantees > that only the aligned part gets through to qcow2_zero(). > > > The patch looks good apart from these nit picks, though. > > Max > >> + assert(QEMU_IS_ALIGNED(offset, s->cluster_size)); >> + assert(QEMU_IS_ALIGNED(count, s->cluster_size)); And since I'm adding assertions that the zero operation is never attempted on unaligned parts, maybe I should also add asserts that discards are never unaligned, perhaps as a prereq patch. I'll wait a bit and see if anyone else has better naming ideas for the functions, before I try to send a v2.
On 06.12.2016 22:26, Eric Blake wrote: > On 12/06/2016 03:01 PM, Max Reitz wrote: >> On 03.12.2016 19:19, Eric Blake wrote: >>> Passing a byte offset, but sector count, when we ultimately >>> want to operate on cluster granularity, is madness. Clean up >>> the interfaces to take byte offset and count. Rename >>> qcow2_discard_clusters() and qcow2_zero_clusters() to the >>> shorter qcow2_discard() and qcow2_zero() to make sure backports >>> don't get confused by changed units. >>> >>> Signed-off-by: Eric Blake <eblake@redhat.com> >>> --- >>> >>> 2.9 material, depends on 'Don't strand clusters near 2G intervals >>> during commit' >>> > >>> @@ -1595,20 +1593,24 @@ static int zero_single_l2(BlockDriverState *bs, uint64_t offset, >>> return nb_clusters; >>> } >>> >>> -int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors, >>> - int flags) >>> +int qcow2_zero(BlockDriverState *bs, uint64_t offset, uint64_t count, >>> + int flags) >> >> Hmm, I personally liked qcow2_zero_clusters() better. qcow2_zero() >> doesn't really express that it means the verb "to zero". >> >> Also, while you are making a good point why the function should be >> renamed, qcow2_zero_clusters() was much more accurate because offset and >> count are expected to be cluster-aligned. >> >> The only alternative I can come up with would be "qcow2_write_zeroes"; >> that at least solves the first issue I have with this, but not the >> second one... > > Maybe qcow2_cluster_zeroize() and qcow2_cluster_discard()? I think qcow2_discard() is fine (it works with any alignment (even though it will only discard whole clusters) and "discard" is mainly used as a verb, so at least I'm not confused there). I like qcow2_cluster_zeroize() if nothing else then for the "zeroize" alone. :-) Max > That gets the > benefit of the rename (to force all callers to use the right semantics), > while still being legible as an object-verb naming: the action > ('discard' or 'zeroize') is performed on 'qcow2 cluster' objects.
On 12/06/2016 03:31 PM, Max Reitz wrote: >>> >>> The only alternative I can come up with would be "qcow2_write_zeroes"; >>> that at least solves the first issue I have with this, but not the >>> second one... >> >> Maybe qcow2_cluster_zeroize() and qcow2_cluster_discard()? > > I think qcow2_discard() is fine (it works with any alignment (even > though it will only discard whole clusters) Except that I think with my recent fix to qcow2_make_empty(), we can now assert that all callers actually pass cluster-aligned values. Hence my other comment that maybe we want to (as a prereq patch) actually assert that callers are aligned, at which point keeping cluster in the name is once again worthwhile. > and "discard" is mainly used > as a verb, so at least I'm not confused there). I like > qcow2_cluster_zeroize() if nothing else then for the "zeroize" alone. :-) Okay, then I have a good idea of what name to use.
diff --git a/block/qcow2.h b/block/qcow2.h index 1823414..a0d169b 100644 --- a/block/qcow2.h +++ b/block/qcow2.h @@ -543,10 +543,10 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs, int compressed_size); int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m); -int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset, - int nb_sectors, enum qcow2_discard_type type, bool full_discard); -int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors, - int flags); +int qcow2_discard(BlockDriverState *bs, uint64_t offset, uint64_t count, + enum qcow2_discard_type type, bool full_discard); +int qcow2_zero(BlockDriverState *bs, uint64_t offset, uint64_t count, + int flags); int qcow2_expand_zero_clusters(BlockDriverState *bs, BlockDriverAmendStatusCB *status_cb, diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 928c1e2..3ee0815 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1511,19 +1511,17 @@ static int discard_single_l2(BlockDriverState *bs, uint64_t offset, return nb_clusters; } -int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset, - int nb_sectors, enum qcow2_discard_type type, bool full_discard) +int qcow2_discard(BlockDriverState *bs, uint64_t offset, uint64_t count, + enum qcow2_discard_type type, bool full_discard) { BDRVQcow2State *s = bs->opaque; uint64_t end_offset; uint64_t nb_clusters; int ret; - end_offset = offset + (nb_sectors << BDRV_SECTOR_BITS); - - /* Round start up and end down */ + /* Round start up and end down to cluster boundary */ + end_offset = start_of_cluster(s, offset + count); offset = align_offset(offset, s->cluster_size); - end_offset = start_of_cluster(s, end_offset); if (offset > end_offset) { return 0; @@ -1595,20 +1593,24 @@ static int zero_single_l2(BlockDriverState *bs, uint64_t offset, return nb_clusters; } -int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors, - int flags) +int qcow2_zero(BlockDriverState *bs, uint64_t offset, uint64_t count, + int flags) { BDRVQcow2State *s = bs->opaque; uint64_t nb_clusters; int ret; + /* Block layer guarantees cluster alignment */ + assert(QEMU_IS_ALIGNED(offset, s->cluster_size)); + assert(QEMU_IS_ALIGNED(count, s->cluster_size)); + /* The zero flag is only supported by version 3 and newer */ if (s->qcow_version < 3) { return -ENOTSUP; } /* Each L2 table is handled by its own loop iteration */ - nb_clusters = size_to_clusters(s, nb_sectors << BDRV_SECTOR_BITS); + nb_clusters = size_to_clusters(s, count); s->cache_discards = true; diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c index 0324243..fd088e5 100644 --- a/block/qcow2-snapshot.c +++ b/block/qcow2-snapshot.c @@ -440,10 +440,9 @@ int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info) /* The VM state isn't needed any more in the active L1 table; in fact, it * hurts by causing expensive COW for the next snapshot. */ - qcow2_discard_clusters(bs, qcow2_vm_state_offset(s), - align_offset(sn->vm_state_size, s->cluster_size) - >> BDRV_SECTOR_BITS, - QCOW2_DISCARD_NEVER, false); + qcow2_discard(bs, qcow2_vm_state_offset(s), + align_offset(sn->vm_state_size, s->cluster_size), + QCOW2_DISCARD_NEVER, false); #ifdef DEBUG_ALLOC { diff --git a/block/qcow2.c b/block/qcow2.c index 369b542..601831f 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2487,7 +2487,7 @@ static coroutine_fn int qcow2_co_pwrite_zeroes(BlockDriverState *bs, trace_qcow2_pwrite_zeroes(qemu_coroutine_self(), offset, count); /* Whatever is left can use real zero clusters */ - ret = qcow2_zero_clusters(bs, offset, count >> BDRV_SECTOR_BITS, flags); + ret = qcow2_zero(bs, offset, count, flags); qemu_co_mutex_unlock(&s->lock); return ret; @@ -2505,8 +2505,7 @@ static coroutine_fn int qcow2_co_pdiscard(BlockDriverState *bs, } qemu_co_mutex_lock(&s->lock); - ret = qcow2_discard_clusters(bs, offset, count >> BDRV_SECTOR_BITS, - QCOW2_DISCARD_REQUEST, false); + ret = qcow2_discard(bs, offset, count, QCOW2_DISCARD_REQUEST, false); qemu_co_mutex_unlock(&s->lock); return ret; } @@ -2807,9 +2806,8 @@ fail: static int qcow2_make_empty(BlockDriverState *bs) { BDRVQcow2State *s = bs->opaque; - uint64_t start_sector; - int sector_step = QEMU_ALIGN_DOWN(INT_MAX / BDRV_SECTOR_SIZE, - s->cluster_size); + uint64_t offset; + int step = QEMU_ALIGN_DOWN(INT_MAX, s->cluster_size); int l1_clusters, ret = 0; l1_clusters = DIV_ROUND_UP(s->l1_size, s->cluster_size / sizeof(uint64_t)); @@ -2826,18 +2824,18 @@ static int qcow2_make_empty(BlockDriverState *bs) /* This fallback code simply discards every active cluster; this is slow, * but works in all cases */ - for (start_sector = 0; start_sector < bs->total_sectors; - start_sector += sector_step) + for (offset = 0; offset < bs->total_sectors * BDRV_SECTOR_SIZE; + offset += step) { /* As this function is generally used after committing an external * snapshot, QCOW2_DISCARD_SNAPSHOT seems appropriate. Also, the * default action for this kind of discard is to pass the discard, * which will ideally result in an actually smaller image file, as * is probably desired. */ - ret = qcow2_discard_clusters(bs, start_sector * BDRV_SECTOR_SIZE, - MIN(sector_step, - bs->total_sectors - start_sector), - QCOW2_DISCARD_SNAPSHOT, true); + ret = qcow2_discard(bs, offset, + MIN(step, + bs->total_sectors * BDRV_SECTOR_SIZE - offset), + QCOW2_DISCARD_SNAPSHOT, true); if (ret < 0) { break; }
Passing a byte offset, but sector count, when we ultimately want to operate on cluster granularity, is madness. Clean up the interfaces to take byte offset and count. Rename qcow2_discard_clusters() and qcow2_zero_clusters() to the shorter qcow2_discard() and qcow2_zero() to make sure backports don't get confused by changed units. Signed-off-by: Eric Blake <eblake@redhat.com> --- 2.9 material, depends on 'Don't strand clusters near 2G intervals during commit' block/qcow2.h | 8 ++++---- block/qcow2-cluster.c | 20 +++++++++++--------- block/qcow2-snapshot.c | 7 +++---- block/qcow2.c | 22 ++++++++++------------ 4 files changed, 28 insertions(+), 29 deletions(-)