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ln: add -L/-P options
* src/ln.c (STAT_LIKE_LINK): Delete. (logical): New flag. (long_options): Add -L, -P. (usage): Mention them. (main): Choose between them. (do_link): Perform correct action. * tests/ln/misc: Move hard-to-sym portion of test... * tests/ln/hard-to-sym: ...into new test, and add more. * tests/Makefile.am (TESTS): Run new test. * NEWS: Document this. * doc/coreutils.texi (link invocation, ln invocation): Likewise. * bootstrap.conf (gnulib_modules): Add linkat.
This commit is contained in:
Eric Blake
parent
fb59d72f0a
commit
efcee783e4
7
NEWS
7
NEWS
@ -32,6 +32,13 @@ GNU coreutils NEWS -*- outline -*-
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last component (possibly via a dangling symlink) can be created,
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since mkdir will succeed in that case.
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** New features
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ln now accepts the options --logical (-L) and --physical (-P),
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added by POSIX 2008. The default behavior is -P on systems like
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GNU/Linux where link(2) creates hard links to symlinks, and -L on
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BSD systems where link(2) follows symlinks.
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** Improvements
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rm: rewrite to use gnulib's fts
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@ -132,6 +132,7 @@ gnulib_modules="
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linebuffer
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link
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link-follow
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linkat
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long-options
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lstat
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maintainer-makefile
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@ -8753,6 +8753,11 @@ On a @acronym{GNU} system, this command acts like @samp{ln --directory
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not specified by @acronym{POSIX}, and the @command{link} command is
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more portable in practice.
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If @var{filename} is a symbolic link, it is unspecified whether
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@var{linkname} will be a hard link to the symbolic link or to the
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target of the symbolic link. Use @command{ln -P} or @command{ln -L}
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to specify which behavior is desired.
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@exitstatus
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@ -8808,8 +8813,10 @@ A @dfn{hard link} is another name for an existing file; the link and the
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original are indistinguishable. Technically speaking, they share the
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same inode, and the inode contains all the information about a
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file---indeed, it is not incorrect to say that the inode @emph{is} the
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file. On all existing implementations, you cannot make a hard link to
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a directory, and hard links cannot cross file system boundaries. (These
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file. Most systems prohibit making a hard link to
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a directory; on those where it is allowed, only the super-user can do
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so (and with caution, since creating a cycle will cause problems to many
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other utilities). Hard links cannot cross file system boundaries. (These
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restrictions are not mandated by @acronym{POSIX}, however.)
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@cindex dereferencing symbolic links
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@ -8821,9 +8828,13 @@ refers to a different file, by name. When most operations (opening,
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reading, writing, and so on) are passed the symbolic link file, the
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kernel automatically @dfn{dereferences} the link and operates on the
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target of the link. But some operations (e.g., removing) work on the
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link file itself, rather than on its target. The owner, group, and
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mode of a symlink are not significant to file access performed through
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the link. @xref{Symbolic Links,,,
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link file itself, rather than on its target. The owner and group of a
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symlink are not significant to file access performed through
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the link, but do have implications on deleting a symbolic link from a
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directory with the restricted deletion bit set. On the GNU system,
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the mode of a symlink has no significance and cannot be changed, but
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on some BSD systems, the mode can be changed and will affect whether
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the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
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libc, The GNU C Library Reference Manual}.
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Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
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@ -8878,6 +8889,14 @@ Remove existing destination files.
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@cindex prompting, and @command{ln}
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Prompt whether to remove existing destination files.
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@item -L
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@itemx --logical
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@opindex -L
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@opindex --logical
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If @option{-s} is not in effect, and the source file is a symbolic
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link, create the hard link to the file referred to by the symbolic
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link, rather than the symbolic link itself.
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@item -n
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@itemx --no-dereference
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@opindex -n
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@ -8899,6 +8918,17 @@ just like a directory.
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This option is weaker than the @option{--no-target-directory}
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(@option{-T}) option, so it has no effect if both options are given.
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@item -P
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@itemx --physical
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@opindex -P
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@opindex --physical
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If @option{-s} is not in effect, and the source file is a symbolic
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link, create the hard link to the symbolic link itself. On platforms
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where this is not supported by the kernel, this option creates a
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symbolic link with identical contents; since symbolic link contents
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cannot be edited, any file name resolution performed through either
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link will be the same as if a hard link had been created.
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@item -s
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@itemx --symbolic
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@opindex -s
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@ -8920,6 +8950,15 @@ Print the name of each file after linking it successfully.
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@end table
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@cindex hard links to symbolic links
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@cindex symbolic links and @command{ln}
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If @option{-L} and @option{-P} are both given, the last one takes
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precedence. If @option{-s} is also given, @option{-L} and @option{-P}
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are silently ignored. If neither option is given, then this
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implementation defaults to @option{-P} if the system @code{link} supports
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hard links to symbolic links (such as the GNU system), and @option{-L}
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if @code{link} follows symbolic links (such as on BSD).
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@exitstatus
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Examples:
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63
src/ln.c
63
src/ln.c
@ -39,26 +39,15 @@
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proper_name ("Mike Parker"), \
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proper_name ("David MacKenzie")
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/* In being careful not even to try to make hard links to directories,
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we have to know whether link(2) follows symlinks. If it does, then
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we have to *stat* the `source' to see if the resulting link would be
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to a directory. Otherwise, we have to use *lstat* so that we allow
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users to make hard links to symlinks-that-point-to-directories. */
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#if LINK_FOLLOWS_SYMLINKS
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# define STAT_LIKE_LINK(File, Stat_buf) \
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stat (File, Stat_buf)
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#else
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# define STAT_LIKE_LINK(File, Stat_buf) \
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lstat (File, Stat_buf)
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#endif
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/* FIXME: document */
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static enum backup_type backup_type;
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/* If true, make symbolic links; otherwise, make hard links. */
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static bool symbolic_link;
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/* If true, hard links are logical rather than physical. */
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static bool logical = !!LINK_FOLLOWS_SYMLINKS;
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/* If true, ask the user before removing existing files. */
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static bool interactive;
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@ -71,7 +60,7 @@ static bool verbose;
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/* If true, allow the superuser to *attempt* to make hard links
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to directories. However, it appears that this option is not useful
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in practice, since even the superuser is prohibited from hard-linking
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directories on most (all?) existing systems. */
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directories on most existing systems (Solaris being an exception). */
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static bool hard_dir_link;
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/* If nonzero, and the specified destination is a symbolic link to a
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@ -99,6 +88,8 @@ static struct option const long_options[] =
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{"interactive", no_argument, NULL, 'i'},
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{"suffix", required_argument, NULL, 'S'},
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{"target-directory", required_argument, NULL, 't'},
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{"logical", no_argument, NULL, 'L'},
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{"physical", no_argument, NULL, 'P'},
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{"symbolic", no_argument, NULL, 's'},
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{"verbose", no_argument, NULL, 'v'},
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{GETOPT_HELP_OPTION_DECL},
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@ -143,18 +134,15 @@ do_link (const char *source, const char *dest)
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bool source_is_dir = false;
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bool ok;
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/* Use stat here instead of lstat.
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On SVR4, link does not follow symlinks, so this check disallows
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making hard links to symlinks that point to directories. Big deal.
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On other systems, link follows symlinks, so this check is right.
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FIXME - POSIX 2008 added the AT_SYMLINK_FOLLOW flag to linkat so
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that we can specify either behavior, via the new options -L
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(hard-link to symlinks) and -P (hard-link to the referent). Once
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gnulib has a decent implementation, we should use it here. */
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if (!symbolic_link)
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{
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if (STAT_LIKE_LINK (source, &source_stats) != 0)
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/* Which stat to use depends on whether linkat will follow the
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symlink. We can't use the shorter
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(logical ? stat : lstat) (source, &source_stats)
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since stat might be a function-like macro. */
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if ((logical ? stat (source, &source_stats)
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: lstat (source, &source_stats))
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!= 0)
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{
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error (0, errno, _("accessing %s"), quote (source));
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return false;
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@ -258,7 +246,9 @@ do_link (const char *source, const char *dest)
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}
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}
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ok = ((symbolic_link ? symlink (source, dest) : link (source, dest))
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ok = ((symbolic_link ? symlink (source, dest)
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: linkat (AT_FDCWD, source, AT_FDCWD, dest,
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logical ? AT_SYMLINK_FOLLOW : 0))
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== 0);
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/* If the attempt to create a link failed and we are removing or
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@ -289,7 +279,9 @@ do_link (const char *source, const char *dest)
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return false;
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}
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ok = ((symbolic_link ? symlink (source, dest) : link (source, dest))
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ok = ((symbolic_link ? symlink (source, dest)
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: linkat (AT_FDCWD, source, AT_FDCWD, dest,
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logical ? AT_SYMLINK_FOLLOW : 0))
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== 0);
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}
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@ -370,9 +362,11 @@ Mandatory arguments to long options are mandatory for short options too.\n\
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-f, --force remove existing destination files\n\
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"), stdout);
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fputs (_("\
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-i, --interactive prompt whether to remove destinations\n\
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-L, --logical make hard links to symbolic link references\n\
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-n, --no-dereference treat destination that is a symlink to a\n\
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directory as if it were a normal file\n\
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-i, --interactive prompt whether to remove destinations\n\
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-P, --physical make hard links directly to symbolic links\n\
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-s, --symbolic make symbolic links instead of hard links\n\
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"), stdout);
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fputs (_("\
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@ -391,6 +385,11 @@ The version control method may be selected via the --backup option or through\n\
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the VERSION_CONTROL environment variable. Here are the values:\n\
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\n\
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"), stdout);
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printf (_("\
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Using -s ignores -L and -P. Otherwise, the last option specified controls\n\
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behavior when the source is a symbolic link, defaulting to %s.\n\
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\n\
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"), LINK_FOLLOWS_SYMLINKS ? "-L" : "-P");
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fputs (_("\
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none, off never make backups (even if --backup is given)\n\
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numbered, t make numbered backups\n\
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@ -430,7 +429,7 @@ main (int argc, char **argv)
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symbolic_link = remove_existing_files = interactive = verbose
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= hard_dir_link = false;
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while ((c = getopt_long (argc, argv, "bdfinst:vFS:T", long_options, NULL))
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while ((c = getopt_long (argc, argv, "bdfinst:vFLPS:T", long_options, NULL))
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!= -1)
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{
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switch (c)
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@ -452,9 +451,15 @@ main (int argc, char **argv)
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remove_existing_files = false;
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interactive = true;
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break;
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case 'L':
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logical = true;
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break;
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case 'n':
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dereference_dest_dir_symlinks = false;
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break;
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case 'P':
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logical = false;
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break;
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case 's':
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symbolic_link = true;
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break;
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@ -344,6 +344,7 @@ TESTS = \
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install/trap \
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ln/backup-1 \
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ln/hard-backup \
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ln/hard-to-sym \
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ln/misc \
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ln/sf-1 \
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ln/slash-decorated-nonexistent-dest \
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82
tests/ln/hard-to-sym
Executable file
82
tests/ln/hard-to-sym
Executable file
@ -0,0 +1,82 @@
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#!/bin/sh
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# Tests for ln -L/-P.
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# Copyright (C) 2009 Free Software Foundation, Inc.
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# 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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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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if test "$VERBOSE" = yes; then
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set -x
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ln --version
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fi
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. $srcdir/test-lib.sh
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fail=0
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# ===================================================
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# ensure -s silently overrides -L, -P
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touch a || framework_failure
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ln -L -s a symlink1 || fail=1
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ln -P -s symlink1 symlink2 || fail=1
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ln -s -L -P symlink2 symlink3 || fail=1
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# ===================================================
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# ensure that -L follows symlinks, and overrides -P
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ln -P -L symlink3 hard-to-a || fail=1
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ls=`ls -lG hard-to-a`x
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case "$ls" in
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*'hard-to-ax') ;;
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*'hard-to-a -> '*x) fail=1 ;;
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*) framework_failure ;;
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esac
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# ===================================================
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# ensure that -P links (or at least duplicates) symlinks, and overrides -L
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ln -L -P symlink3 hard-to-3 || fail=1
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ls=`ls -lG hard-to-3`x
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case "$ls" in
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*'hard-to-3 -> symlink2x') ;;
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*'hard-to-3x') fail=1 ;;
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*'hard-to-3 -> '*x) fail=1 ;;
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*) framework_failure ;;
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esac
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# ===================================================
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# Create a hard link to a dangling symlink.
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ln -s /no-such-dir || framework_failure
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ln -L no-such-dir hard-to-dangle 2>err && fail=1
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case `cat err` in
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*' accessing `no-such-dir'\':*) ;;
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*) fail=1 ;;
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esac
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ln -P no-such-dir hard-to-dangle || fail=1
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# ===================================================
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# Create a hard link to a symlink to a directory.
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mkdir d || framework_failure
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ln -s d link-to-dir || framework_failure
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ln -L link-to-dir hard-to-dir-link 2>err && fail=1
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case `cat err` in
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*': `link-to-dir'\'': hard link not allowed for directory'*) ;;
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*) fail=1 ;;
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esac
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ln -P link-to-dir/ hard-to-dir-link 2>err && fail=1
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case `cat err` in
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*': `link-to-dir/'\'': hard link not allowed for directory'*) ;;
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*) fail=1 ;;
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esac
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ln -P link-to-dir hard-to-dir-link || fail=1
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Exit $fail
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@ -107,29 +107,6 @@ touch a b || framework_failure
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ln b b~ || framework_failure
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ln -f --b=simple a b || fail=1
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# ===================================================
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# determine if link(2) follows symlinks on this system
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touch a || framework_failure
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ln -s a symlink || framework_failure
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ln symlink hard-to-sym > /dev/null 2>&1 || framework_failure
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ls=`ls -lG hard-to-sym`x
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case "$ls" in
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*'hard-to-symx') link_follows_symlink=yes ;;
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*'hard-to-sym -> ax') link_follows_symlink=no ;;
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*) framework_failure ;;
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esac
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if test $link_follows_symlink = no; then
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# Create a hard link to a dangling symlink.
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# This is not portable. At least sunos4.1.4 and OpenBSD 2.3 fail this test.
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# They get this:
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# ln: cannot create hard link `hard-to-dangle' to `no-such-dir': \
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# No such file or directory
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#
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ln -s /no-such-dir || fail=1
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ln no-such-dir hard-to-dangle > /dev/null 2>&1 || fail=1
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fi
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rm -rf a symlink hard-to-sym hard-to-dangle
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# ===================================================
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# Make sure ln can make simple backups.
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