| Message ID | 20170627192458.15519-5-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Jun 27, 2017 at 02:24:42PM -0500, Eric Blake wrote: > We are gradually converting to byte-based interfaces, as they are > easier to reason about than sector-based. Change the internal > loop iteration of streaming to track by bytes instead of sectors > (although we are still guaranteed that we iterate by steps that > are sector-aligned). > > Signed-off-by: Eric Blake <eblake@redhat.com> > Reviewed-by: John Snow <jsnow@redhat.com> > Reviewed-by: Jeff Cody <jcody@redhat.com> > --- > v2: no change > --- > block/stream.c | 24 ++++++++++-------------- > 1 file changed, 10 insertions(+), 14 deletions(-) > > diff --git a/block/stream.c b/block/stream.c > index 746d525..2f9618b 100644 > --- a/block/stream.c > +++ b/block/stream.c > @@ -108,12 +108,11 @@ static void coroutine_fn stream_run(void *opaque) > BlockBackend *blk = s->common.blk; > BlockDriverState *bs = blk_bs(blk); > BlockDriverState *base = s->base; > - int64_t sector_num = 0; > - int64_t end = -1; > + int64_t offset = 0; > uint64_t delay_ns = 0; > int error = 0; > int ret = 0; > - int n = 0; > + int n = 0; /* sectors */ > void *buf; > > if (!bs->backing) { > @@ -126,7 +125,6 @@ static void coroutine_fn stream_run(void *opaque) > goto out; > } > > - end = s->common.len >> BDRV_SECTOR_BITS; > buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE); > > /* Turn on copy-on-read for the whole block device so that guest read > @@ -138,7 +136,7 @@ static void coroutine_fn stream_run(void *opaque) > bdrv_enable_copy_on_read(bs); > } > > - for (sector_num = 0; sector_num < end; sector_num += n) { > + for ( ; offset < s->common.len; offset += n * BDRV_SECTOR_SIZE) { > bool copy; > > /* Note that even when no rate limit is applied we need to yield > @@ -151,28 +149,26 @@ static void coroutine_fn stream_run(void *opaque) > > copy = false; > > - ret = bdrv_is_allocated(bs, sector_num, > + ret = bdrv_is_allocated(bs, offset / BDRV_SECTOR_SIZE, > STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE, &n); > if (ret == 1) { > /* Allocated in the top, no need to copy. */ > } else if (ret >= 0) { > /* Copy if allocated in the intermediate images. Limit to the > - * known-unallocated area [sector_num, sector_num+n). */ > + * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE). */ > ret = bdrv_is_allocated_above(backing_bs(bs), base, > - sector_num, n, &n); > + offset / BDRV_SECTOR_SIZE, n, &n); > > /* Finish early if end of backing file has been reached */ > if (ret == 0 && n == 0) { > - n = end - sector_num; > + n = (s->common.len - offset) / BDRV_SECTOR_SIZE; > } > > copy = (ret == 1); > } > - trace_stream_one_iteration(s, sector_num * BDRV_SECTOR_SIZE, > - n * BDRV_SECTOR_SIZE, ret); > + trace_stream_one_iteration(s, offset, n * BDRV_SECTOR_SIZE, ret); > if (copy) { > - ret = stream_populate(blk, sector_num * BDRV_SECTOR_SIZE, > - n * BDRV_SECTOR_SIZE, buf); > + ret = stream_populate(blk, offset, n * BDRV_SECTOR_SIZE, buf); > } > if (ret < 0) { > BlockErrorAction action = > @@ -211,7 +207,7 @@ out: > /* Modify backing chain and close BDSes in main loop */ > data = g_malloc(sizeof(*data)); > data->ret = ret; > - data->reached_end = sector_num == end; > + data->reached_end = offset == s->common.len; > block_job_defer_to_main_loop(&s->common, stream_complete, data); > } > > -- > 2.9.4 >
Am 27.06.2017 um 21:24 hat Eric Blake geschrieben: > We are gradually converting to byte-based interfaces, as they are > easier to reason about than sector-based. Change the internal > loop iteration of streaming to track by bytes instead of sectors > (although we are still guaranteed that we iterate by steps that > are sector-aligned). > > Signed-off-by: Eric Blake <eblake@redhat.com> > Reviewed-by: John Snow <jsnow@redhat.com> > > --- > v2: no change > --- > block/stream.c | 24 ++++++++++-------------- > 1 file changed, 10 insertions(+), 14 deletions(-) > > diff --git a/block/stream.c b/block/stream.c > index 746d525..2f9618b 100644 > --- a/block/stream.c > +++ b/block/stream.c > @@ -108,12 +108,11 @@ static void coroutine_fn stream_run(void *opaque) > BlockBackend *blk = s->common.blk; > BlockDriverState *bs = blk_bs(blk); > BlockDriverState *base = s->base; > - int64_t sector_num = 0; > - int64_t end = -1; Here, end was initialised to -1. This made a differnce for early 'goto out' paths because otherwise data->reached_end would incorrectly be true in stream_complete. Because we also check data->ret, I think the only case where it actually makes a difference is for the !bs->backing case: This used to result in data->reached_end == false, but now it ends up as true. This is because s->common.len hasn't been set yet, so it is still 0. Kevin
On 07/04/2017 10:00 AM, Kevin Wolf wrote: > Am 27.06.2017 um 21:24 hat Eric Blake geschrieben: >> We are gradually converting to byte-based interfaces, as they are >> easier to reason about than sector-based. Change the internal >> loop iteration of streaming to track by bytes instead of sectors >> (although we are still guaranteed that we iterate by steps that >> are sector-aligned). >> >> Signed-off-by: Eric Blake <eblake@redhat.com> >> Reviewed-by: John Snow <jsnow@redhat.com> >> >> --- >> v2: no change >> --- >> block/stream.c | 24 ++++++++++-------------- >> 1 file changed, 10 insertions(+), 14 deletions(-) >> >> diff --git a/block/stream.c b/block/stream.c >> index 746d525..2f9618b 100644 >> --- a/block/stream.c >> +++ b/block/stream.c >> @@ -108,12 +108,11 @@ static void coroutine_fn stream_run(void *opaque) >> BlockBackend *blk = s->common.blk; >> BlockDriverState *bs = blk_bs(blk); >> BlockDriverState *base = s->base; >> - int64_t sector_num = 0; >> - int64_t end = -1; > > Here, end was initialised to -1. This made a differnce for early 'goto > out' paths because otherwise data->reached_end would incorrectly be true > in stream_complete. Oh, good call. > > Because we also check data->ret, I think the only case where it actually > makes a difference is for the !bs->backing case: This used to result in > data->reached_end == false, but now it ends up as true. This is because > s->common.len hasn't been set yet, so it is still 0. When !bs->backing, ret is 0; so that means my commit message is wrong about there being no semantic change. But remember, when !bs->backing, stream is a no-op (there was no backing file to stream into the current layer, anyways) - so which do we want, declaring that the operation never reached the end (odd, since we did nothing), or that it is complete? In other words, is this something where I should fix the semantics (perhaps as a separate bug-fix patch), or where I need to fix this patch to preserve existing semantics? The next code reached is stream_complete(). Before my patch, it skipped the main body of the function (because !data->reached_end); with my patch, we are now calling bdrv_change_backing_file() (presumably a no-op when there is no backing?)
Am 05.07.2017 um 14:13 hat Eric Blake geschrieben: > On 07/04/2017 10:00 AM, Kevin Wolf wrote: > > Am 27.06.2017 um 21:24 hat Eric Blake geschrieben: > >> We are gradually converting to byte-based interfaces, as they are > >> easier to reason about than sector-based. Change the internal > >> loop iteration of streaming to track by bytes instead of sectors > >> (although we are still guaranteed that we iterate by steps that > >> are sector-aligned). > >> > >> Signed-off-by: Eric Blake <eblake@redhat.com> > >> Reviewed-by: John Snow <jsnow@redhat.com> > >> > >> --- > >> v2: no change > >> --- > >> block/stream.c | 24 ++++++++++-------------- > >> 1 file changed, 10 insertions(+), 14 deletions(-) > >> > >> diff --git a/block/stream.c b/block/stream.c > >> index 746d525..2f9618b 100644 > >> --- a/block/stream.c > >> +++ b/block/stream.c > >> @@ -108,12 +108,11 @@ static void coroutine_fn stream_run(void *opaque) > >> BlockBackend *blk = s->common.blk; > >> BlockDriverState *bs = blk_bs(blk); > >> BlockDriverState *base = s->base; > >> - int64_t sector_num = 0; > >> - int64_t end = -1; > > > > Here, end was initialised to -1. This made a differnce for early 'goto > > out' paths because otherwise data->reached_end would incorrectly be true > > in stream_complete. > > Oh, good call. > > > > > Because we also check data->ret, I think the only case where it actually > > makes a difference is for the !bs->backing case: This used to result in > > data->reached_end == false, but now it ends up as true. This is because > > s->common.len hasn't been set yet, so it is still 0. > > When !bs->backing, ret is 0; so that means my commit message is wrong > about there being no semantic change. But remember, when !bs->backing, > stream is a no-op (there was no backing file to stream into the current > layer, anyways) - so which do we want, declaring that the operation > never reached the end (odd, since we did nothing), or that it is > complete? In other words, is this something where I should fix the > semantics (perhaps as a separate bug-fix patch), or where I need to fix > this patch to preserve existing semantics? > > The next code reached is stream_complete(). Before my patch, it skipped > the main body of the function (because !data->reached_end); with my > patch, we are now calling bdrv_change_backing_file() (presumably a no-op > when there is no backing?) Effectively probably yes, but it involves another write+flush for rewriting the qcow2 header (even though nothing is expected to change in it). But if we wanted to avoid this, I think we could just directly check bs->backing in stream_complete(). So I wonder why data->reached_end even exists in the first place. Kevin
diff --git a/block/stream.c b/block/stream.c index 746d525..2f9618b 100644 --- a/block/stream.c +++ b/block/stream.c @@ -108,12 +108,11 @@ static void coroutine_fn stream_run(void *opaque) BlockBackend *blk = s->common.blk; BlockDriverState *bs = blk_bs(blk); BlockDriverState *base = s->base; - int64_t sector_num = 0; - int64_t end = -1; + int64_t offset = 0; uint64_t delay_ns = 0; int error = 0; int ret = 0; - int n = 0; + int n = 0; /* sectors */ void *buf; if (!bs->backing) { @@ -126,7 +125,6 @@ static void coroutine_fn stream_run(void *opaque) goto out; } - end = s->common.len >> BDRV_SECTOR_BITS; buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE); /* Turn on copy-on-read for the whole block device so that guest read @@ -138,7 +136,7 @@ static void coroutine_fn stream_run(void *opaque) bdrv_enable_copy_on_read(bs); } - for (sector_num = 0; sector_num < end; sector_num += n) { + for ( ; offset < s->common.len; offset += n * BDRV_SECTOR_SIZE) { bool copy; /* Note that even when no rate limit is applied we need to yield @@ -151,28 +149,26 @@ static void coroutine_fn stream_run(void *opaque) copy = false; - ret = bdrv_is_allocated(bs, sector_num, + ret = bdrv_is_allocated(bs, offset / BDRV_SECTOR_SIZE, STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE, &n); if (ret == 1) { /* Allocated in the top, no need to copy. */ } else if (ret >= 0) { /* Copy if allocated in the intermediate images. Limit to the - * known-unallocated area [sector_num, sector_num+n). */ + * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE). */ ret = bdrv_is_allocated_above(backing_bs(bs), base, - sector_num, n, &n); + offset / BDRV_SECTOR_SIZE, n, &n); /* Finish early if end of backing file has been reached */ if (ret == 0 && n == 0) { - n = end - sector_num; + n = (s->common.len - offset) / BDRV_SECTOR_SIZE; } copy = (ret == 1); } - trace_stream_one_iteration(s, sector_num * BDRV_SECTOR_SIZE, - n * BDRV_SECTOR_SIZE, ret); + trace_stream_one_iteration(s, offset, n * BDRV_SECTOR_SIZE, ret); if (copy) { - ret = stream_populate(blk, sector_num * BDRV_SECTOR_SIZE, - n * BDRV_SECTOR_SIZE, buf); + ret = stream_populate(blk, offset, n * BDRV_SECTOR_SIZE, buf); } if (ret < 0) { BlockErrorAction action = @@ -211,7 +207,7 @@ out: /* Modify backing chain and close BDSes in main loop */ data = g_malloc(sizeof(*data)); data->ret = ret; - data->reached_end = sector_num == end; + data->reached_end = offset == s->common.len; block_job_defer_to_main_loop(&s->common, stream_complete, data); }