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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>
88 lines
3.4 KiB
C
88 lines
3.4 KiB
C
#ifndef SCM_FILESYS_H
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#define SCM_FILESYS_H
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/* Copyright 1995,1997-2001,2006,2008-2011,2013,2018,2021
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Free Software Foundation, Inc.
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This file is part of Guile.
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Guile is free software: you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published
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by the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Guile is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with Guile. If not, see
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<https://www.gnu.org/licenses/>. */
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#include <libguile/error.h>
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SCM_API scm_t_bits scm_tc16_dir;
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#define SCM_DIR_FLAG_OPEN (1L << 0)
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#define SCM_DIRP(x) (SCM_HAS_TYP16 (x, scm_tc16_dir))
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#define SCM_DIR_OPEN_P(x) (SCM_SMOB_FLAGS (x) & SCM_DIR_FLAG_OPEN)
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#define SCM_VALIDATE_DIR(pos, port) \
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SCM_MAKE_VALIDATE_MSG (pos, port, DIRP, "directory port")
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SCM_API SCM scm_chown (SCM object, SCM owner, SCM group);
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SCM_API SCM scm_chownat (SCM dir, SCM object, SCM owner, SCM group, SCM flags);
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SCM_API SCM scm_chmod (SCM object, SCM mode);
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SCM_API SCM scm_chmodat (SCM dir, SCM pathname, SCM mode, SCM flags);
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SCM_API SCM scm_umask (SCM mode);
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SCM_API SCM scm_open_fdes (SCM path, SCM flags, SCM mode);
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SCM_API SCM scm_open_fdes_at (SCM dir, SCM path, SCM flags, SCM mode);
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SCM_API SCM scm_open (SCM path, SCM flags, SCM mode);
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SCM_API SCM scm_openat (SCM dir, SCM path, SCM flags, SCM mode);
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SCM_API SCM scm_close (SCM fd_or_port);
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SCM_API SCM scm_close_fdes (SCM fd);
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SCM_API SCM scm_stat (SCM object, SCM exception_on_error);
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SCM_API SCM scm_statat (SCM dir, SCM filename, SCM flags);
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SCM_API SCM scm_link (SCM oldpath, SCM newpath);
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SCM_API SCM scm_rename (SCM oldname, SCM newname);
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SCM_API SCM scm_renameat (SCM olddir, SCM oldname, SCM newdir, SCM newname);
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SCM_API SCM scm_delete_file (SCM str);
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SCM_API SCM scm_delete_file_at (SCM dir, SCM str, SCM flags);
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SCM_API SCM scm_mkdir (SCM path, SCM mode);
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SCM_API SCM scm_mkdirat (SCM dir, SCM path, SCM mode);
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SCM_API SCM scm_rmdir (SCM path);
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SCM_API SCM scm_directory_stream_p (SCM obj);
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SCM_API SCM scm_opendir (SCM dirname);
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SCM_API SCM scm_readdir (SCM port);
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SCM_API SCM scm_rewinddir (SCM port);
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SCM_API SCM scm_closedir (SCM port);
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SCM_API SCM scm_chdir (SCM str);
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SCM_API SCM scm_getcwd (void);
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SCM_API SCM scm_select (SCM reads, SCM writes, SCM excepts, SCM secs, SCM msecs);
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SCM_API SCM scm_fcntl (SCM object, SCM cmd, SCM value);
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SCM_API SCM scm_fsync (SCM object);
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SCM_API SCM scm_symlink (SCM oldpath, SCM newpath);
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SCM_API SCM scm_symlinkat (SCM dir, SCM oldpath, SCM newpath);
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SCM_API SCM scm_readlink (SCM path);
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SCM_API SCM scm_lstat (SCM str);
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SCM_API SCM scm_copy_file (SCM oldfile, SCM newfile);
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SCM_INTERNAL SCM scm_copy_file2 (SCM oldfile, SCM newfile, SCM rest);
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SCM_API SCM scm_mkstemp (SCM tmpl);
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SCM_API SCM scm_mkdtemp (SCM tmpl);
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SCM_API SCM scm_dirname (SCM filename);
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SCM_API SCM scm_basename (SCM filename, SCM suffix);
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SCM_API SCM scm_canonicalize_path (SCM path);
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SCM_API SCM scm_sendfile (SCM out, SCM in, SCM count, SCM offset);
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SCM_INTERNAL SCM scm_i_relativize_path (SCM path, SCM in_path);
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SCM_INTERNAL void scm_init_filesys (void);
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#endif /* SCM_FILESYS_H */
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