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

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