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e1690f3fd2
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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| .. | ||
| .gitignore | ||
| api-binding.texi | ||
| api-control.texi | ||
| api-coverage.texi | ||
| api-data.texi | ||
| api-debug.texi | ||
| api-deprecated.texi | ||
| api-evaluation.texi | ||
| api-foreign-objects.texi | ||
| api-foreign.texi | ||
| api-i18n.texi | ||
| api-init.texi | ||
| api-io.texi | ||
| api-lalr.texi | ||
| api-languages.texi | ||
| api-macros.texi | ||
| api-memory.texi | ||
| api-modules.texi | ||
| api-options.texi | ||
| api-overview.texi | ||
| api-peg.texi | ||
| api-procedures.texi | ||
| api-regex.texi | ||
| api-scheduling.texi | ||
| api-scm.texi | ||
| api-smobs.texi | ||
| api-snarf.texi | ||
| api-undocumented.texi | ||
| api-utility.texi | ||
| api.txt | ||
| ChangeLog-2008 | ||
| ChangeLog-goops-2008 | ||
| ChangeLog-guile-doc-ref | ||
| compiler.texi | ||
| curried.texi | ||
| data-rep.texi | ||
| effective-version.texi.in | ||
| expect.texi | ||
| fdl.texi | ||
| gds.dia | ||
| gds.eps | ||
| gds.pdf | ||
| gds.txt | ||
| goops-tutorial.texi | ||
| goops.texi | ||
| guile-invoke.texi | ||
| guile.texi | ||
| hierarchy.dot | ||
| hierarchy.eps | ||
| hierarchy.pdf | ||
| hierarchy.png | ||
| hierarchy.txt | ||
| history.texi | ||
| indices.texi | ||
| intro.texi | ||
| libguile-autoconf.texi | ||
| libguile-concepts.texi | ||
| libguile-extensions.texi | ||
| libguile-foreign-objects.texi | ||
| libguile-linking.texi | ||
| libguile-parallel.texi | ||
| libguile-program.texi | ||
| libguile-snarf.texi | ||
| Makefile.am | ||
| match.texi | ||
| misc-modules.texi | ||
| mod-getopt-long.texi | ||
| mop.text | ||
| new-docstrings.texi | ||
| posix.texi | ||
| preface.texi | ||
| r6rs.texi | ||
| r7rs.texi | ||
| repl-modules.texi | ||
| scheme-ideas.texi | ||
| scheme-indices.texi | ||
| scheme-intro.texi | ||
| scheme-reading.texi | ||
| scheme-scripts.texi | ||
| scheme-using.texi | ||
| scheme.dia | ||
| scheme.eps | ||
| scheme.pdf | ||
| scheme.txt | ||
| scsh.texi | ||
| slib.texi | ||
| srfi-modules.texi | ||
| statprof.texi | ||
| sxml-match.texi | ||
| sxml.texi | ||
| texinfo.texi | ||
| tools.texi | ||
| tour.texi | ||
| vm.texi | ||
| web.texi | ||
