CentOS - Dec 2010 - Issues with stat() call on CentOS5 vs CentOS4

Dear CentOS,

I have recently upgraded several servers from CentOS4 to CentOS5 and I am
noticing a strange change to the stat() call. I have written a very
small program to test and show the behavior. I am calling stat()
against a file which is exported from my NAS and mounted with 32k
read/write sizes.

[dougalb at centos4 tmp]$ cat my_stat.c
#include <unistd.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>

int main(int argc, char **argv)
{
   if(argc != 2)
       return 1;

   struct stat fileStat;
   if(stat(argv[1],&fileStat) < 0)
       return 1;

   printf("Block size: \t\t%d\n",fileStat.st_blksize);

   return 0;
}

[dougalb at centos4 tmp]$
[dougalb at centos4 tmp]$ gcc -o my_stat.exe my_stat.c
[dougalb at centos4 tmp]$
[dougalb at centos4 tmp]$ ./my_stat.exe /mnt/nas/testfile
Block size:             32768
[dougalb at centos4 tmp]$
[dougalb at centos4 tmp]$ cat /etc/redhat-release
CentOS release 4.7 (Final)
[dougalb at centos4 tmp]$

[dougalb at centos5 tmp]$ ./my_stat.exe /mnt/nas/testfile
Block size:             4096
[dougalb at centos5 tmp]$
[dougalb at centos5 tmp]$ cat /etc/redhat-release
CentOS release 5.5 (Final)
[dougalb at centos5 tmp]$

On CentOS5 it is reporting 4k block sizes when it should report 32k. Has
anyone seen this or aware of what is causing this change in behavior?

Kind regards,

Dougal

On 10/12/10 18:23, Dougal Ballantyne wrote:
> Dear CentOS,
>
> I have recently upgraded several servers from CentOS4 to CentOS5 and I am
> noticing a strange change to the stat() call. I have written a very
> small program to test and show the behavior. I am calling stat()
> against a file which is exported from my NAS and mounted with 32k
> read/write sizes.
>
> [dougalb at centos4 tmp]$ cat my_stat.c
> #include<unistd.h>
> #include<stdio.h>
> #include<sys/stat.h>
> #include<sys/types.h>
>
> int main(int argc, char **argv)
> {
>     if(argc != 2)
>         return 1;
>
>     struct stat fileStat;
>     if(stat(argv[1],&fileStat)<  0)
>         return 1;
>
>     printf("Block size: \t\t%d\n",fileStat.st_blksize);
>
>     return 0;
> }
>
> [dougalb at centos4 tmp]$
> [dougalb at centos4 tmp]$ gcc -o my_stat.exe my_stat.c
> [dougalb at centos4 tmp]$
> [dougalb at centos4 tmp]$ ./my_stat.exe /mnt/nas/testfile
> Block size:             32768
> [dougalb at centos4 tmp]$
> [dougalb at centos4 tmp]$ cat /etc/redhat-release
> CentOS release 4.7 (Final)
> [dougalb at centos4 tmp]$
>
> [dougalb at centos5 tmp]$ ./my_stat.exe /mnt/nas/testfile
> Block size:             4096
> [dougalb at centos5 tmp]$
> [dougalb at centos5 tmp]$ cat /etc/redhat-release
> CentOS release 5.5 (Final)
> [dougalb at centos5 tmp]$
>
> On CentOS5 it is reporting 4k block sizes when it should report 32k. Has
> anyone seen this or aware of what is causing this change in behavior?
What kind of network file system is used to mount your NAS?


kind regards,

David Sommerseth

Dougal Ballantyne wrote:
> 
> I have recently upgraded several servers from CentOS4 to CentOS5 and I am
> noticing a strange change to the stat() call. I have written a very
> small program to test and show the behavior. I am calling stat()
> against a file which is exported from my NAS and mounted with 32k
> read/write sizes.
The man page for stat(2) states:
> Use of the st_blocks and st_blksize fields may be less portable.  (They
> were  introduced  in  BSD.  The interpretation differs between systems,
> and possibly on a single system when NFS mounts are involved.)
Also, the kernel patch at 
<http://android.git.kernel.org/?p=kernel/common.git;a=commitdiff_plain;h=ba52de123d454b57369f291348266d86f4b35070>
states:
> This eliminates the i_blksize field from struct inode.  Filesystems that
want
> to provide a per-inode st_blksize can do so by providing their own getattr
> routine instead of using the generic_fillattr() function.
> 
> Note that some filesystems were providing pretty much random (and
incorrect)
> values for i_blksize.
The CentOS5 kernel contains the above patch, which removes the setting 
of st_blksize by the NFS client kernel code - previously, the NFS client 
  code set st_blksize to the wsize (write size)

The default for blksize is PAGE_CACHE_SIZE (in fs/stat.c) - which is 4096

However, with CentOS6/RHEL6, it appears st_blksize has reverted back to 
wsize - the default is now (in fs/stat.c) "1 <<
inode->i_blkbits"

As a test, I rebuild a CentOS5 kernel with the above change - and stat() 
  now reports the wsize for st_blksize ...

I don't know if this is a bug or a feature

James Pearson