[Libguestfs] [PATCH v2 0/4] file: Zero for block devices and older file systems

[Nir Soffer]

On Fri, Aug 3, 2018 at 10:28 PM Nir Soffer <nirsof at gmail.com> wrote:

> This is the third version to support efficient zero for block devices
> on older kernels (e.g. RHEL 7.5), and file systems that do not support
> yet FALLOC_FS_ZERO_RANGE (e.g. NFS 4.2).
>
> Changes since v2:
> - Revert file_can_trim change, since it is too late to change the value
>   after negotiation. Changing the capability dinamically may be useful
>   internally, but it should be done via other means.
> - Do not depend on FALLOC_FL_* when including <linux/fs.h>.
> - Add common/includes/isaligned.h for is_aligned helper, implemented
>   in a more efficient way with bitwise math.
> - If getting sector size fail, fall back to safe guess instead of
>   hard failure.
> - More efficient alignment check using bitwise math.
> - For BLKZEROOUT, treat ENOTTY as EOPNOTSUPP. Theoretically possible
>   with a mix of new headers and old or strangely configured kernel.
> - Use default multi line comment style.
> - Fix few typos in comments and commit message
>
> Issues to explore later:
> - Eric suggested to use the new FALLOC_FL_NO_HIDE_STALE. Requires
>   benchmarking with a system supporting this flag.
> - Eric suggested to use tri-state for can_* flags. I don't see a need at
>   this point.
> - Eric suggested to add can_zero. I'm not sure about the semantics of
>   this, and it has the same issue of can_trim, reporting dynamic value.
>
> v2 was here:
> https://www.redhat.com/archives/libguestfs/2018-August/msg00025.html
>
> Changes since v1:
> - Split to smaller patches
> - Skip linux only includes on other systems
> - Skip code using BLKZEROOUT if the macro is not defined
> - Try BLKZEROOUT only if the offset and count are aligned to device
>   sector size.
> - initialize h->can_* properly. Before they were uninitialized if
>   FALLOC_FL_* macros were not defined.
> - Use new h->can_punch_hole in file_can_trim, so now we report the
>   actual capability once we detected it.
> - Use h->can_punch_hole in file_trim, so we try only once if the
>   operation is not supported.
>
> v1 was here:
> https://www.redhat.com/archives/libguestfs/2018-July/msg00084.html
>
> Nir Soffer (4):
>   file: Avoid unsupported fallocate() calls
>   file: Support zero without ZERO_RANGE
>   common: Add isaligned helper module
>   file: Zero for block devices on old kernels
>
>  common/include/isaligned.h |  50 ++++++++++
>  plugins/file/Makefile.am   |   3 +-
>  plugins/file/file.c        | 182 +++++++++++++++++++++++++++++--------
>  3 files changed, 196 insertions(+), 39 deletions(-)
>  create mode 100644 common/include/isaligned.h
>
> --
> 2.17.1
>
>
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