| @node unlinkat |
| @section @code{unlinkat} |
| @findex unlinkat |
| |
| POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlinkat.html} |
| |
| Gnulib module: unlinkat |
| |
| Portability problems fixed by Gnulib: |
| @itemize |
| @item |
| This function is missing on some platforms: |
| glibc 2.3.6, Mac OS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 3.8, Minix 3.1.8, |
| AIX 5.1, HP-UX 11, IRIX 6.5, Cygwin 1.5.x, mingw, MSVC 14. |
| But the replacement function is not safe to be used in libraries and is not multithread-safe. |
| @item |
| This function is declared in @code{<fcntl.h>}, not in @code{<unistd.h>}, |
| on some platforms: |
| Cygwin 1.7.1, Android 4.3. |
| @item |
| On Mac OS X 10.10, in a writable HFS mount, @code{unlinkat(fd, "..", 0)} succeeds |
| without doing anything. |
| @item |
| Some systems mistakenly succeed on @code{unlinkat(fd,"file/",flag)}: |
| GNU/Hurd, Solaris 9. |
| @end itemize |
| |
| Portability problems not fixed by Gnulib: |
| @itemize |
| @item |
| When @code{unlinkat(fd,name,AT_REMOVEDIR)} fails because the specified |
| directory is not empty, the @code{errno} value is system dependent. |
| @item |
| POSIX requires that @code{unlinkdir(fd,"link-to-empty/",AT_REMOVEDIR)} |
| remove @file{empty} and leave @file{link-to-empty} as a dangling |
| symlink. This is counter-intuitive, so some systems fail with |
| @code{ENOTDIR} instead: |
| glibc |
| @item |
| Some systems allow a superuser to unlink directories, even though this |
| can cause file system corruption. The error given if a process is not |
| permitted to unlink directories varies across implementations; it is |
| not always the POSIX value of @code{EPERM}. Meanwhile, if a process |
| has the ability to unlink directories, POSIX requires that |
| @code{unlinkat(fd,"symlink-to-dir/",0)} remove @file{dir} and leave |
| @file{symlink-to-dir} dangling; this behavior is counter-intuitive. |
| The gnulib module @code{unlinkdir} can help determine whether code must be |
| cautious of unlinking directories. |
| @item |
| Removing an open file is non-portable: On Unix this allows the programs that |
| have the file already open to continue working with it; the file's storage |
| is only freed when the no process has the file open any more. On Windows, |
| the attempt to remove an open file fails. |
| @end itemize |