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86c22b430f
Cygwin 1.7.1 placed symlinkat and unlinkat in the wrong headers (due to a bug in the Linux man pages). * lib/unistd.in.h (includes): Pick up headers needed for cygwin. * doc/posix-functions/unlinkat.texi (unlinkat): Document the bug. * doc/posix-functions/symlinkat.texi (symlinkat): Likewise. Signed-off-by: Eric Blake <ebb9@byu.net>
52 lines
2.0 KiB
Plaintext
52 lines
2.0 KiB
Plaintext
@node unlinkat
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@section @code{unlinkat}
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@findex unlinkat
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POSIX specification: @url{http://www.opengroup.org/onlinepubs/9699919799/functions/unlinkat.html}
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Gnulib module: openat
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Portability problems fixed by Gnulib:
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@itemize
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@item
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This function is missing on some platforms:
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glibc 2.3.6, MacOS X 10.3, FreeBSD 6.0, NetBSD 3.0, OpenBSD 3.8, AIX
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5.1, HP-UX 11, IRIX 6.5, OSF/1 5.1, Cygwin 1.5.x, mingw, Interix 3.5, BeOS.
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But the replacement function is not safe to be used in libraries and is not multithread-safe.
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@item
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Some systems mistakenly succeed on @code{unlinkat(fd,"file/",flag)}:
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GNU/Hurd, Solaris 9.
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@item
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Some platforms declare this function in @code{fcntl.h} instead of
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@code{unistd.h}:
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Cygwin 1.7.1.
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@end itemize
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Portability problems not fixed by Gnulib:
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@itemize
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@item
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When @code{unlinkat(fd,name,AT_REMOVEDIR)} fails because the specified
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directory is not empty, the @code{errno} value is system dependent.
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@item
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POSIX requires that @code{unlinkdir(fd,"link-to-empty/",AT_REMOVEDIR)}
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remove @file{empty} and leave @file{link-to-empty} as a dangling
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symlink. This is counter-intuitive, so some systems fail with
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@code{ENOTDIR} instead:
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glibc
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@item
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Some systems allow a superuser to unlink directories, even though this
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can cause file system corruption. The error given if a process is not
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permitted to unlink directories varies across implementations; it is
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not always the POSIX value of @code{EPERM}. Meanwhile, if a process
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has the ability to unlink directories, POSIX requires that
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@code{unlinkat(fd,"symlink-to-dir/",0)} remove @file{dir} and leave
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@file{symlink-to-dir} dangling; this behavior is counter-intuitive.
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The gnulib module unlinkdir can help determine whether code must be
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cautious of unlinking directories.
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@item
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Removing an open file is non-portable: On Unix this allows the programs that
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have the file already open to continue working with it; the file's storage
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is only freed when the no process has the file open any more. On Windows,
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the attempt to remove an open file fails.
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@end itemize
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