From: Eric Blake Date: Mon, 21 Sep 2009 20:40:20 +0000 (-0600) Subject: readlink: document portability issue with symlink length X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0510d19e64a0c3cfdd7ebe31866be9b45229590a;hp=5835d9b52879c334f16e747c54be8ec9c62e8536;p=pspp readlink: document portability issue with symlink length Per comments in areadlink, ERANGE on a too-small buffer is expected on some platforms; making the readlink module guarantee GNU behavior of truncated contents is counter-productive, since we would be duplicating areadlink to learn a-priori how large to make the buffer, and since truncated contents are not as useful. * doc/posix-functions/lstat.texi (lstat): Mention that some file systems have bogus st_size on symlinks, and mention the areadlink-with-size module. * doc/posix-functions/fstatat.texi (fstatat): Likewise. * doc/posix-functions/readlink.texi (readlink): Mention the areadlink module, and ERANGE failure. * doc/posix-functions/readlinkat.texi (readlinkat): Likewise. * tests/test-readlink.c (main): Relax test for AIX, HP-UX. Signed-off-by: Eric Blake --- diff --git a/ChangeLog b/ChangeLog index 9337f56d0b..618f1c9ad7 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,5 +1,15 @@ 2009-09-23 Eric Blake + readlink: document portability issue with symlink length + * doc/posix-functions/lstat.texi (lstat): Mention that some file + systems have bogus st_size on symlinks, and mention the + areadlink-with-size module. + * doc/posix-functions/fstatat.texi (fstatat): Likewise. + * doc/posix-functions/readlink.texi (readlink): Mention the + areadlink module, and ERANGE failure. + * doc/posix-functions/readlinkat.texi (readlinkat): Likewise. + * tests/test-readlink.c (main): Relax test for AIX, HP-UX. + readlink: fix Solaris 9 bug with trailing slash * lib/readlink.c (rpl_readlink): Work around trailing slash bug. * m4/readlink.m4 (gl_FUNC_READLINK): Detect the bug. diff --git a/doc/posix-functions/fstatat.texi b/doc/posix-functions/fstatat.texi index d1c4c83419..b96fc4d54e 100644 --- a/doc/posix-functions/fstatat.texi +++ b/doc/posix-functions/fstatat.texi @@ -31,4 +31,8 @@ not correctly report the size of files or block devices larger than 2 GB. The fix is to use the @code{AC_SYS_LARGEFILE} macro. @item On Windows platforms (excluding Cygwin), @code{st_ino} is always 0. +@item +On some filesystems, @code{st_size} contains bogus information for +symlinks; use the gnulib module areadlink-with-size for a better way +to get symlink contents. @end itemize diff --git a/doc/posix-functions/lstat.texi b/doc/posix-functions/lstat.texi index dbe31f8636..328b896c90 100644 --- a/doc/posix-functions/lstat.texi +++ b/doc/posix-functions/lstat.texi @@ -35,4 +35,8 @@ portably replace @code{stat} via an object-like macro. Therefore, expressions such as @code{(islnk ? lstat : stat) (name, buf)} are not portable, and should instead be written @code{islnk ? lstat (name, buf) : stat (name, buf)}. +@item +On some filesystems, @code{st_size} contains bogus information for +symlinks; use the gnulib module areadlink-with-size for a better way +to get symlink contents. @end itemize diff --git a/doc/posix-functions/readlink.texi b/doc/posix-functions/readlink.texi index 959f62d7a3..b1218f6c26 100644 --- a/doc/posix-functions/readlink.texi +++ b/doc/posix-functions/readlink.texi @@ -31,4 +31,12 @@ directories, Cygwin sets @code{errno} to @code{ENOENT} or @code{EIO} instead of When @code{readlink} is called on a file that is not a symbolic link: Irix may set @code{errno} to @code{ENXIO} instead of @code{EINVAL}. Cygwin may set errno to @code{EACCES} instead of @code{EINVAL}. +@item +Symlink contents do not always have a trailing null byte, and there is +no indication if symlink contents were truncated if the return value +matches the length. Furthermore, AIX 5.1 and HP-UX 11 set +@code{errno} to @code{ERANGE} rather than returning truncated +contents, and Linux sets @code{errno} to @code{EINVAL} if the +requested length is zero. Use the gnulib module areadlink for +improved ability to read symlink contents. @end itemize diff --git a/doc/posix-functions/readlinkat.texi b/doc/posix-functions/readlinkat.texi index b64b443fd7..65f088fa59 100644 --- a/doc/posix-functions/readlinkat.texi +++ b/doc/posix-functions/readlinkat.texi @@ -28,4 +28,12 @@ directories, Cygwin sets @code{errno} to @code{ENOENT} or @code{EIO} instead of When @code{readlink} is called on a file that is not a symbolic link: Irix may set @code{errno} to @code{ENXIO} instead of @code{EINVAL}. Cygwin may set errno to @code{EACCES} instead of @code{EINVAL}. +@item +Symlink contents do not always have a trailing null byte, and there is +no indication if symlink contents were truncated if the return value +matches the length. Furthermore, AIX 5.1 and HP-UX 11 set +@code{errno} to @code{ERANGE} rather than returning truncated +contents, and Linux sets @code{errno} to @code{EINVAL} if the +requested length is zero. Use the gnulib module areadlink for +improved ability to read symlink contents. @end itemize diff --git a/tests/test-readlink.c b/tests/test-readlink.c index f0f921eddd..97a6788b93 100644 --- a/tests/test-readlink.c +++ b/tests/test-readlink.c @@ -97,10 +97,21 @@ main () { size_t len = strlen (BASE "dir"); /* When passing too small of a buffer, expect the truncated - length. However, a size of 0 is not portable enough to - test. */ - ASSERT (readlink (BASE "link", buf, 1) == 1); - ASSERT (buf[0] == BASE[0]); + length, or an ERANGE failure. However, a size of 0 is not + portable enough to test. */ + ssize_t result; + errno = 0; + result = readlink (BASE "link", buf, 1); + if (result == -1) + { + ASSERT (errno == ERANGE); + ASSERT (buf[0] == (char) 0xff); + } + else + { + ASSERT (result == 1); + ASSERT (buf[0] == BASE[0]); + } ASSERT (buf[1] == (char) 0xff); ASSERT (readlink (BASE "link", buf, len) == len); ASSERT (strncmp (buf, BASE "dir", len) == 0);