| Message ID | 20190918095144.955-8-mreitz@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: Add @exact parameter to bdrv_co_truncate() | expand |
On Wed, 2019-09-18 at 11:51 +0200, Max Reitz wrote: > This is a change in behavior, so all instances need a good > justification. The comments added here should explain my reasoning. > > qed already had a comment that suggests it always expected > bdrv_truncate()/blk_truncate() to behave as if exact=true were passed > (c743849bee7 came eight months before 55b949c8476), so it was simply > broken until now. > > Signed-off-by: Max Reitz <mreitz@redhat.com> > --- > block/parallels.c | 11 +++++++++-- > block/qcow2.c | 6 +++++- > block/qed.c | 2 +- > qemu-img.c | 7 ++++++- > qemu-io-cmds.c | 7 ++++++- > 5 files changed, 27 insertions(+), 6 deletions(-) > > diff --git a/block/parallels.c b/block/parallels.c > index a1a92c97a4..603211f83c 100644 > --- a/block/parallels.c > +++ b/block/parallels.c > @@ -487,7 +487,12 @@ static int coroutine_fn parallels_co_check(BlockDriverState *bs, > res->leaks += count; > if (fix & BDRV_FIX_LEAKS) { > Error *local_err = NULL; > - ret = bdrv_truncate(bs->file, res->image_end_offset, false, > + > + /* > + * In order to really repair the image, we must shrink it. > + * That means we have to pass exact=true. > + */ > + ret = bdrv_truncate(bs->file, res->image_end_offset, true, > PREALLOC_MODE_OFF, &local_err); I am not familiar with the parallels format, but in theory, a partial fix is better that nothing. > if (ret < 0) { > error_report_err(local_err); > @@ -880,7 +885,9 @@ static void parallels_close(BlockDriverState *bs) > if ((bs->open_flags & BDRV_O_RDWR) && !(bs->open_flags & BDRV_O_INACTIVE)) { > s->header->inuse = 0; > parallels_update_header(bs); > - bdrv_truncate(bs->file, s->data_end << BDRV_SECTOR_BITS, false, > + > + /* errors are ignored, so we might as well pass exact=true */ > + bdrv_truncate(bs->file, s->data_end << BDRV_SECTOR_BITS, true, > PREALLOC_MODE_OFF, NULL); Fair enough. > } > > diff --git a/block/qcow2.c b/block/qcow2.c > index 4ef19dd29a..eba165de7f 100644 > --- a/block/qcow2.c > +++ b/block/qcow2.c > @@ -5057,7 +5057,11 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts, > return ret; > } > > - ret = blk_truncate(blk, new_size, false, PREALLOC_MODE_OFF, errp); > + /* > + * Amending image options should ensure that the image has > + * exactly the given new values, so pass exact=true here. > + */ Agree. > + ret = blk_truncate(blk, new_size, true, PREALLOC_MODE_OFF, errp); > blk_unref(blk); > if (ret < 0) { > return ret; > diff --git a/block/qed.c b/block/qed.c > index 7c2a65af40..8005cfc305 100644 > --- a/block/qed.c > +++ b/block/qed.c > @@ -674,7 +674,7 @@ static int coroutine_fn bdrv_qed_co_create(BlockdevCreateOptions *opts, > l1_size = header.cluster_size * header.table_size; > > /* File must start empty and grow, check truncate is supported */ I would update the above comment, with something like "QED format requires the underlying file to have the exact expected length, which is 0 on creation" Or something similar. > - ret = blk_truncate(blk, 0, false, PREALLOC_MODE_OFF, errp); > + ret = blk_truncate(blk, 0, true, PREALLOC_MODE_OFF, errp); > if (ret < 0) { > goto out; > } > diff --git a/qemu-img.c b/qemu-img.c > index f8694f4f72..a3169b6113 100644 > --- a/qemu-img.c > +++ b/qemu-img.c > @@ -3823,7 +3823,12 @@ static int img_resize(int argc, char **argv) > } > } > > - ret = blk_truncate(blk, total_size, false, prealloc, &err); > + /* > + * The user expects the image to have the desired size after > + * resizing, so pass @exact=true. It is of no use to report > + * success when the image has not actually been resized. > + */ Agree. > + ret = blk_truncate(blk, total_size, true, prealloc, &err); > if (ret < 0) { > error_report_err(err); > goto out; > diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c > index 5e9017c979..1b7e700020 100644 > --- a/qemu-io-cmds.c > +++ b/qemu-io-cmds.c > @@ -1710,7 +1710,12 @@ static int truncate_f(BlockBackend *blk, int argc, char **argv) > return offset; > } > > - ret = blk_truncate(blk, offset, false, PREALLOC_MODE_OFF, &local_err); > + /* > + * qemu-io is a debugging tool, so let us be strict here and pass > + * exact=true. It is better to err on the "emit more errors" side > + * than to be overly permissive. > + */ Also agree. > + ret = blk_truncate(blk, offset, true, PREALLOC_MODE_OFF, &local_err); > if (ret < 0) { > error_report_err(local_err); > return ret; Other than few nitpicks which probably aren't important, Reviewed-by: Maxim Levitsky <mlevitsky@redhat.com> Best regards, Maxim Levitsky
On 18.09.19 22:52, Maxim Levitsky wrote: > On Wed, 2019-09-18 at 11:51 +0200, Max Reitz wrote: >> This is a change in behavior, so all instances need a good >> justification. The comments added here should explain my reasoning. >> >> qed already had a comment that suggests it always expected >> bdrv_truncate()/blk_truncate() to behave as if exact=true were passed >> (c743849bee7 came eight months before 55b949c8476), so it was simply >> broken until now. >> >> Signed-off-by: Max Reitz <mreitz@redhat.com> >> --- >> block/parallels.c | 11 +++++++++-- >> block/qcow2.c | 6 +++++- >> block/qed.c | 2 +- >> qemu-img.c | 7 ++++++- >> qemu-io-cmds.c | 7 ++++++- >> 5 files changed, 27 insertions(+), 6 deletions(-) [...] >> diff --git a/block/qed.c b/block/qed.c >> index 7c2a65af40..8005cfc305 100644 >> --- a/block/qed.c >> +++ b/block/qed.c >> @@ -674,7 +674,7 @@ static int coroutine_fn bdrv_qed_co_create(BlockdevCreateOptions *opts, >> l1_size = header.cluster_size * header.table_size; >> >> /* File must start empty and grow, check truncate is supported */ > I would update the above comment, with something like > > "QED format requires the underlying file to have the exact expected length, > which is 0 on creation" > Or something similar. I’ll change it to: The QED format associates file length with allocation status, so a new file (which is empty) must have a length of 0. Hope that’s OK. :-) Max
diff --git a/block/parallels.c b/block/parallels.c index a1a92c97a4..603211f83c 100644 --- a/block/parallels.c +++ b/block/parallels.c @@ -487,7 +487,12 @@ static int coroutine_fn parallels_co_check(BlockDriverState *bs, res->leaks += count; if (fix & BDRV_FIX_LEAKS) { Error *local_err = NULL; - ret = bdrv_truncate(bs->file, res->image_end_offset, false, + + /* + * In order to really repair the image, we must shrink it. + * That means we have to pass exact=true. + */ + ret = bdrv_truncate(bs->file, res->image_end_offset, true, PREALLOC_MODE_OFF, &local_err); if (ret < 0) { error_report_err(local_err); @@ -880,7 +885,9 @@ static void parallels_close(BlockDriverState *bs) if ((bs->open_flags & BDRV_O_RDWR) && !(bs->open_flags & BDRV_O_INACTIVE)) { s->header->inuse = 0; parallels_update_header(bs); - bdrv_truncate(bs->file, s->data_end << BDRV_SECTOR_BITS, false, + + /* errors are ignored, so we might as well pass exact=true */ + bdrv_truncate(bs->file, s->data_end << BDRV_SECTOR_BITS, true, PREALLOC_MODE_OFF, NULL); } diff --git a/block/qcow2.c b/block/qcow2.c index 4ef19dd29a..eba165de7f 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -5057,7 +5057,11 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts, return ret; } - ret = blk_truncate(blk, new_size, false, PREALLOC_MODE_OFF, errp); + /* + * Amending image options should ensure that the image has + * exactly the given new values, so pass exact=true here. + */ + ret = blk_truncate(blk, new_size, true, PREALLOC_MODE_OFF, errp); blk_unref(blk); if (ret < 0) { return ret; diff --git a/block/qed.c b/block/qed.c index 7c2a65af40..8005cfc305 100644 --- a/block/qed.c +++ b/block/qed.c @@ -674,7 +674,7 @@ static int coroutine_fn bdrv_qed_co_create(BlockdevCreateOptions *opts, l1_size = header.cluster_size * header.table_size; /* File must start empty and grow, check truncate is supported */ - ret = blk_truncate(blk, 0, false, PREALLOC_MODE_OFF, errp); + ret = blk_truncate(blk, 0, true, PREALLOC_MODE_OFF, errp); if (ret < 0) { goto out; } diff --git a/qemu-img.c b/qemu-img.c index f8694f4f72..a3169b6113 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -3823,7 +3823,12 @@ static int img_resize(int argc, char **argv) } } - ret = blk_truncate(blk, total_size, false, prealloc, &err); + /* + * The user expects the image to have the desired size after + * resizing, so pass @exact=true. It is of no use to report + * success when the image has not actually been resized. + */ + ret = blk_truncate(blk, total_size, true, prealloc, &err); if (ret < 0) { error_report_err(err); goto out; diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c index 5e9017c979..1b7e700020 100644 --- a/qemu-io-cmds.c +++ b/qemu-io-cmds.c @@ -1710,7 +1710,12 @@ static int truncate_f(BlockBackend *blk, int argc, char **argv) return offset; } - ret = blk_truncate(blk, offset, false, PREALLOC_MODE_OFF, &local_err); + /* + * qemu-io is a debugging tool, so let us be strict here and pass + * exact=true. It is better to err on the "emit more errors" side + * than to be overly permissive. + */ + ret = blk_truncate(blk, offset, true, PREALLOC_MODE_OFF, &local_err); if (ret < 0) { error_report_err(local_err); return ret;
This is a change in behavior, so all instances need a good justification. The comments added here should explain my reasoning. qed already had a comment that suggests it always expected bdrv_truncate()/blk_truncate() to behave as if exact=true were passed (c743849bee7 came eight months before 55b949c8476), so it was simply broken until now. Signed-off-by: Max Reitz <mreitz@redhat.com> --- block/parallels.c | 11 +++++++++-- block/qcow2.c | 6 +++++- block/qed.c | 2 +- qemu-img.c | 7 ++++++- qemu-io-cmds.c | 7 ++++++- 5 files changed, 27 insertions(+), 6 deletions(-)