through dm.c, and
> into dm-linear.c to see how to make things clearest. Although I would
> like to have the same semantics for every seek function, maybe in the
> end your suggestion will make the code clearer. Let's see.
Keeping lseek semantics may require a couple more lines
On Wed, Apr 03, 2024 at 10:11:47AM -0400, Stefan Hajnoczi wrote:
...
> > > +static loff_t dm_blk_do_seek_hole_data(struct dm_table *table, loff_t
> > > offset,
> > > + int whence)
> > > +{
> > > + struct dm_target *ti;
> > > + loff_t end;
> > > +
> > > + /* Loop when the end of a target is
her the community would be open to
introducing new SEEK_* constants to allow orthogonality between
searching for zeroes (known to read as zero, whether or not it was
allocated) vs. sparseness (known to be unallocated, whether or not it
reads as zero), where the existing SEEK_HOLE seeks for both p
would prove that even though block devices
generally operate on a minimum granularity of a sector, lseek() still
gives byte-accurate results for a random offset that falls in the
middle of a sector, and doesn't accidentally round down reporting an
offset less than the value passed in to the request.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
antics you have in 4/9 (although in 6/9 I argue that
having all of the dm callbacks return ti->begin + ti->len instead of
-ENXIO might make logic easier for iterating through consecutive ti,
and then convert to -ENXIO only in the caller).
> +}
> +
> static struct target_type thin_ta
e second), but without that
in place, I worry that you are missing logic bugs for when there is
more than one table in the overall dm (as evidenced by my review in
4/9).
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
ess = linear_dax_direct_access,
> .dax_zero_page_range = linear_dax_zero_page_range,
> .dax_recovery_write = linear_dax_recovery_write,
> + .seek_hole_data = linear_seek_hole_data,
> };
>
> int __init dm_linear_init(void)
> --
> 2.44.0
>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
equivalent of
lseek(dm, 0, SEEK_END). If you make my above suggested changes, we
will iterate through the do loop once more at EOF, and
dm_table_find_target() will then fail to match at which point we do
get the desired -ENXIO for both SEEK_HOLE and SEEK_DATA.
> +
> + return offset;
> +}
> +
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
clean, even on a 32-bit
system where lseek is different than lseek64? (I honestly have no
idea if python always uses 64-bit seek even on 32-bit systems,
although I would be surprised if it were not)
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
> return -EINVAL;
> }
> -
> +
> /* Hide this loop device for serialization. */
> ret = mutex_lock_killable(&loop_ctl_mutex);
> if (ret)
Unrelated whitespace change?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
t; Signed-off-by: Stefan Hajnoczi
> ---
> include/linux/blkdev.h | 7 +++
> block/fops.c | 43 +-
> 2 files changed, 49 insertions(+), 1 deletion(-)
>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
Replying to myself,
On Thu, Mar 28, 2024 at 05:17:18PM -0500, Eric Blake wrote:
> On Thu, Mar 28, 2024 at 04:39:01PM -0400, Stefan Hajnoczi wrote:
> > cp(1) and backup tools use llseek(SEEK_HOLE/SEEK_DATA) to skip holes in
> > files.
>
> >
> > In the block
set, while an in-range SEEK_DATA returns the device size)?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
ate mode 100644 tools/testing/selftests/block_seek_hole/config
> create mode 100755 tools/testing/selftests/block_seek_hole/dm_thin.sh
> create mode 100755 tools/testing/selftests/block_seek_hole/dm_zero.sh
> create mode 100755 tools/testing/selftests/block_seek_hole/map_holes.py
> create mode 100755 tools/testing/selftests/block_seek_hole/test.py
>
> --
> 2.44.0
>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
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