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@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: %d
",fileStat.st_blksize);

return 0;
}

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

[dougalb@centos5 tmp]$ ./my_stat.exe /mnt/nas/testfile
Block size: 4096
[dougalb@centos5 tmp]$
[dougalb@centos5 tmp]$ cat /etc/redhat-release
CentOS release 5.5 (Final)
[dougalb@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
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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@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: %d
",fileStat.st_blksize);
>
> return 0;
> }
>
> [dougalb@centos4 tmp]$
> [dougalb@centos4 tmp]$ gcc -o my_stat.exe my_stat.c
> [dougalb@centos4 tmp]$
> [dougalb@centos4 tmp]$ ./my_stat.exe /mnt/nas/testfile
> Block size: 32768
> [dougalb@centos4 tmp]$
> [dougalb@centos4 tmp]$ cat /etc/redhat-release
> CentOS release 4.7 (Final)
> [dougalb@centos4 tmp]$
>
> [dougalb@centos5 tmp]$ ./my_stat.exe /mnt/nas/testfile
> Block size: 4096
> [dougalb@centos5 tmp]$
> [dougalb@centos5 tmp]$ cat /etc/redhat-release
> CentOS release 5.5 (Final)
> [dougalb@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

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Hi David,

I am using NFSv3. Sorry, should have said that!

-Dougal

On Fri, Dec 10, 2010 at 2:06 PM, David Sommerseth
<dazo@users.sourceforge.net> wrote:
> 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@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: %d
",fileStat.st_blksize);
>>
>> * * return 0;
>> }
>>
>> [dougalb@centos4 tmp]$
>> [dougalb@centos4 tmp]$ gcc -o my_stat.exe my_stat.c
>> [dougalb@centos4 tmp]$
>> [dougalb@centos4 tmp]$ ./my_stat.exe /mnt/nas/testfile
>> Block size: * * * * * * 32768
>> [dougalb@centos4 tmp]$
>> [dougalb@centos4 tmp]$ cat /etc/redhat-release
>> CentOS release 4.7 (Final)
>> [dougalb@centos4 tmp]$
>>
>> [dougalb@centos5 tmp]$ ./my_stat.exe /mnt/nas/testfile
>> Block size: * * * * * * 4096
>> [dougalb@centos5 tmp]$
>> [dougalb@centos5 tmp]$ cat /etc/redhat-release
>> CentOS release 5.5 (Final)
>> [dougalb@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
>
> _______________________________________________
> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>
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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=ba52de123d454b5736 9f291348266d86f4b35070>
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
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CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos

James,

Thank you. This is very helpful. It does seem like a very strange
change in behavior between CentOS/RHEL4,5 & 6.

I am rebuilding a kernel with only i_blksize restored for NFS. Don't
like having to change the kernel but might be needed to keep
consistency accross releases.

-Dougal

On Mon, Dec 13, 2010 at 9:30 AM, James Pearson
<james-p@moving-picture.com> wrote:
> 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=ba52de123d454b5736 9f291348266d86f4b35070>
> 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
> _______________________________________________
> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>
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Dougal Ballantyne wrote:
> James,
>
> Thank you. This is very helpful. It does seem like a very strange
> change in behavior between CentOS/RHEL4,5 & 6.
>
> I am rebuilding a kernel with only i_blksize restored for NFS. Don't
> like having to change the kernel but might be needed to keep
> consistency accross releases.

Maybe you should open a Bugzilla report with Red Hat?

James Pearson
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