Re: [PATCH] mkdir.2: Add EMLINK error

[Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hello Maxin,

On Mon, Jun 21, 2010 at 5:48 PM, Maxin John <maxin.john-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Dear Michael,
>
> While executing the below given program in ext3 file system, I came
> across the EMLINK error in mkdir(2) syscall.
>
> # cat test_max_directories.c
>
> #include <stdio.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <stdlib.h>
> #include <errno.h>
>
> int main()
> {
>    char dirname[50];
>    int i;
>    /* The max number of subdirectories in one directory for ext3 is 32000 */
>    int limit = 32001;
>
>    for (i = 0; i < limit; i++) {
>        sprintf(dirname, "testdir%d", i);
>        if ((mkdir(dirname, 00777)) == -1) {
>            perror("Error in creating directory!");
>            printf("errno = %d\n", errno);
>            exit(1);
>        }
>    }
>    return 0;
> }
>
>
> # ./a.out
> Error in creating directory!: Too many links
> errno = 29
>
> An strace of this execution shows that the mkdir(2) call generates an
> EMLINK error when it reaches the limit of  maximum number of sub
> directories in one directory
>
> #strace ./a.out
> -----------------------------------
> .....
> mkdir("testdir31998", 0777)             = -1 EMLINK (Too many links)
> dup(2)                                  = 3
> fcntl64(3, F_GETFL)                     = 0x8002 (flags O_RDWR|O_LARGEFILE)
> brk(0)                                  = 0x804a000
> brk(0x806b000)                          = 0x806b000
> fstat64(3, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
> 0) = 0xb7f71000
> _llseek(3, 0, 0xbffc3078, SEEK_CUR)     = -1 ESPIPE (Illegal seek)
> write(3, "Error in creating directory!: To"..., 45Error in creating
> directory!: Too many links
> ) = 45
> close(3)                                = 0
> munmap(0xb7f71000, 4096)                = 0
> fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
> 0) = 0xb7f71000
> write(1, "errno = 29\n", 11errno = 29
> )            = 11
> exit_group(1)                           = ?
> Process 16246 detached
> -----------------------------------
>
> However, reference to EMLINK is not present in the mkdir(2) man page.
> The following patch adds the EMLINK error in the man page of mkdir(2).
>
> Kindly let me know if there are any issues.

Thanks for the very precise and well supported bug report!

Yes, the page should be fixed. However:

> -------
>
> diff --git a/man2/mkdir.2 b/man2/mkdir.2
> index e6cb28c..d01bafd 100644
> --- a/man2/mkdir.2
> +++ b/man2/mkdir.2
> @@ -73,6 +73,10 @@ is a symbolic link, dangling or not.
>  Too many symbolic links were encountered in resolving
>  .IR pathname .
>  .TP
> +.B EMLINK
> +The new directory cannot be created because the number of sub directories
> +in a directory is limited to LINK_MAX defined by the file system.
> +.TP
>  .B ENAMETOOLONG
>  .IR pathname " was too long."
>  .TP
>
> -------

It's slightly more accurate to talk of links than subdirectories, I
think )that's what POSIX does). So instead, I applied the below patch.

Thanks!

Michael


--- a/man2/mkdir.2
+++ b/man2/mkdir.2
@@ -73,6 +73,10 @@ is a symbolic link, dangling or not.
 Too many symbolic links were encountered in resolving
 .IR pathname .
 .TP
+.B EMLINK
+The number of links to the parent directory would exceed
+.BR LINK_MAX .
+.TP
 .B ENAMETOOLONG
 .IR pathname " was too long."
 .TP




-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface" http://blog.man7.org/
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