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authorTomas Volf <~@wolfsden.cz>2024-01-24 20:14:32 +0100
committerLudovic Courtès <ludo@gnu.org>2024-03-12 14:04:41 +0100
commite1690f3fd251d69b3687ec12c6f4b41034047f0f (patch)
tree8e03c78273eb8f2d96229f679ec5b4573ab73afa /module/system/base/optimize.scm
parent9e0f03c5fd36764827c8bb03887f14640c883b70 (diff)
downloadguile-e1690f3fd251d69b3687ec12c6f4b41034047f0f.tar.gz
Add copy-on-write support to scm_copy_file.
On modern file-systems (BTRFS, ZFS) it is possible to copy a file using copy-on-write method. For large files it has the advantage of being much faster and saving disk space (since identical extents are not duplicated). This feature is stable and for example coreutils' `cp' does use it automatically (see --reflink). This commit adds support for this feature into our copy-file procedure. Same as `cp', it defaults to 'auto, meaning the copy-on-write is attempted, and in case of failure the regular copy is performed. No tests are provided, because the behavior depends on the system, underlying file-system and its configuration. That makes it challenging to write a test for it. Manual testing was performed instead: $ btrfs filesystem du /tmp/cow* Total Exclusive Set shared Filename 36.00KiB 36.00KiB 0.00B /tmp/cow $ cat cow-test.scm (copy-file "/tmp/cow" "/tmp/cow-unspecified") (copy-file "/tmp/cow" "/tmp/cow-always" #:copy-on-write 'always) (copy-file "/tmp/cow" "/tmp/cow-auto" #:copy-on-write 'auto) (copy-file "/tmp/cow" "/tmp/cow-never" #:copy-on-write 'never) (copy-file "/tmp/cow" "/dev/shm/cow-unspecified") (copy-file "/tmp/cow" "/dev/shm/cow-auto" #:copy-on-write 'auto) (copy-file "/tmp/cow" "/dev/shm/cow-never" #:copy-on-write 'never) $ ./meta/guile -s cow-test.scm $ btrfs filesystem du /tmp/cow* Total Exclusive Set shared Filename 36.00KiB 0.00B 36.00KiB /tmp/cow 36.00KiB 0.00B 36.00KiB /tmp/cow-always 36.00KiB 0.00B 36.00KiB /tmp/cow-auto 36.00KiB 36.00KiB 0.00B /tmp/cow-never 36.00KiB 0.00B 36.00KiB /tmp/cow-unspecified $ sha1sum /tmp/cow* /dev/shm/cow* 4c665f87b5dc2e7d26279c4b48968d085e1ace32 /tmp/cow 4c665f87b5dc2e7d26279c4b48968d085e1ace32 /tmp/cow-always 4c665f87b5dc2e7d26279c4b48968d085e1ace32 /tmp/cow-auto 4c665f87b5dc2e7d26279c4b48968d085e1ace32 /tmp/cow-never 4c665f87b5dc2e7d26279c4b48968d085e1ace32 /tmp/cow-unspecified 4c665f87b5dc2e7d26279c4b48968d085e1ace32 /dev/shm/cow-auto 4c665f87b5dc2e7d26279c4b48968d085e1ace32 /dev/shm/cow-never 4c665f87b5dc2e7d26279c4b48968d085e1ace32 /dev/shm/cow-unspecified This commit also adds to new failure modes for (copy-file). Failure to copy-on-write when 'always was passed in: scheme@(guile-user)> (copy-file "/tmp/cow" "/dev/shm/cow" #:copy-on-write 'always) ice-9/boot-9.scm:1676:22: In procedure raise-exception: In procedure copy-file: copy-on-write failed: Invalid cross-device link Passing in invalid value for the #:copy-on-write keyword argument: scheme@(guile-user)> (copy-file "/tmp/cow" "/dev/shm/cow" #:copy-on-write 'nevr) ice-9/boot-9.scm:1676:22: In procedure raise-exception: In procedure copy-file: invalid value for #:copy-on-write: nevr * NEWS: Add note for copy-file supporting copy-on-write. * configure.ac: Check for linux/fs.h. * doc/ref/posix.texi (File System)[copy-file]: Document the new signature. * libguile/filesys.c (clone_file): New function cloning a file using FICLONE, if supported. (k_copy_on_write): New keyword. (sym_always, sym_auto, sym_never): New symbols. (scm_copy_file2): Renamed from scm_copy_file. New #:copy-on-write keyword argument. Attempt copy-on-write copy by default. (scm_copy_file): Call scm_copy_file2. * libguile/filesys.h: Add scm_copy_file2 as SCM_INTERNAL. Signed-off-by: Ludovic Courtès <ludo@gnu.org>
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