[PATCH] mkdir.2: Add EMLINK error

[PATCH] mkdir.2: Add EMLINK error

[Maxin John]

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.

Best Regards,
Maxin B. John
www.maxinbjohn.info

Signed-off-by: Maxin B. John <maxinbjohn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

-------

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

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

[Maxin John]

Hi,

A quick google search shows that the sus v3 version of mkdir(2) has
reference to EMLINK error

http://www.opengroup.org/onlinepubs/000095399/functions/mkdir.html
"
[EMLINK]
    The link count of the parent directory would exceed {LINK_MAX}.
"
Please let me know your opinion on this.

Best Regards,
Maxin B. John

On Mon, Jun 21, 2010 at 9:18 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.
>
> Best Regards,
> Maxin B. John
> www.maxinbjohn.info
>
> Signed-off-by: Maxin B. John <maxinbjohn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>
> -------
>
> 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
>
> -------
>
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Re: [PATCH] mkdir.2: Add EMLINK error

[Maxin John]

ping ...



On Thu, Jun 24, 2010 at 10:22 AM, Maxin John <maxin.john-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Hi,
>
> A quick google search shows that the sus v3 version of mkdir(2) has
> reference to EMLINK error
>
> http://www.opengroup.org/onlinepubs/000095399/functions/mkdir.html
> "
> [EMLINK]
>    The link count of the parent directory would exceed {LINK_MAX}.
> "
> Please let me know your opinion on this.
>
> Best Regards,
> Maxin B. John
>
> On Mon, Jun 21, 2010 at 9:18 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.
>>
>> Best Regards,
>> Maxin B. John
>> www.maxinbjohn.info
>>
>> Signed-off-by: Maxin B. John <maxinbjohn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>
>> -------
>>
>> 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
>>
>> -------
>>
>
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Re: [PATCH] mkdir.2: Add EMLINK error

[Michael Kerrisk]

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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