setting allocation size in cifs/smb3

[Steve French]

To Windows 8.1 it appears to round to 4K boundaries when shrinking but
also not extend the allocation size when allocating beyond end of file
as the documentation would imply

[sfrench at localhost cifs-2.6]$ stat /mnt/test/4M ; fallocate -n -l
5400000 /mnt/test/4M ; sleep 3 ; stat /mnt/test/4M ; fallocate -n -l
10000 /mnt/test/4M ; sleep 2; stat /mnt/test/4M
  File: ‘/mnt/test/4M’
  Size: 4194304   Blocks: 8192       IO Block: 16384  regular file
Device: 26h/38d Inode: 1407374883618316  Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Context: system_u:object_r:cifs_t:s0
Access: 2014-07-21 14:36:20.249486200 -0500
Modify: 2014-07-21 14:36:20.389204200 -0500
Change: 2014-07-21 14:36:20.389204200 -0500
 Birth: -
  File: ‘/mnt/test/4M’
  Size: 4194304   Blocks: 8192       IO Block: 16384  regular file
Device: 26h/38d Inode: 1407374883618316  Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Context: system_u:object_r:cifs_t:s0
Access: 2014-07-21 14:36:20.249486200 -0500
Modify: 2014-07-21 14:38:01.677837600 -0500
Change: 2014-07-21 14:38:01.677837600 -0500
 Birth: -
  File: ‘/mnt/test/4M’
  Size: 12288     Blocks: 24         IO Block: 16384  regular file
Device: 26h/38d Inode: 1407374883618316  Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Context: system_u:object_r:cifs_t:s0
Access: 2014-07-21 14:36:20.249486200 -0500
Modify: 2014-07-21 14:38:04.693266400 -0500
Change: 2014-07-21 14:38:04.693266400 -0500
 Birth: -

On Mon, Jul 21, 2014 at 2:27 PM, Steve French <smfrench at gmail.com> wrote:
> So depending on the file sizes and with strict allocate enabled in
> smb.conf it does shrink the file (I will also experiment with e.g.
> allocation roundup size)
>
> What I was trying to do was extend allocation for a 4MB file to 5.4MB,
> shrink it to 10K (which ended up shrinking it to 1MB for the Samba
> case).
>
> [sfrench at localhost cifs-2.6]$ stat /mnt/test/4M ; fallocate -n -l
> 5400000 /mnt/test/4M ; sleep 3 ; stat /mnt/test/4M ; fallocate -n -l
> 10000 /mnt/test/4M ; sleep 2; stat /mnt/test/4M
>   File: ‘/mnt/test/4M’
>   Size: 4194304   Blocks: 8192       IO Block: 16384  regular file
> Device: 26h/38d Inode: 393820      Links: 1
> Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
> Context: system_u:object_r:cifs_t:s0
> Access: 2014-07-21 14:19:30.596249500 -0500
> Modify: 2014-07-21 14:19:30.731591000 -0500
> Change: 2014-07-21 14:19:30.731591000 -0500
>  Birth: -
>
>   File: ‘/mnt/test/4M’   (after fallocate 5400000)
>   Size: 4194304   Blocks: 8192       IO Block: 16384  regular file
> Device: 26h/38d Inode: 393820      Links: 1
> Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
> Context: system_u:object_r:cifs_t:s0
> Access: 2014-07-21 14:19:30.596249500 -0500
> Modify: 2014-07-21 14:20:17.141270500 -0500
> Change: 2014-07-21 14:20:17.141270500 -0500
>  Birth: -
>
>   File: ‘/mnt/test/4M’  (after fallocate 10000)
>   Size: 1048576   Blocks: 2048       IO Block: 16384  regular file
> Device: 26h/38d Inode: 393820      Links: 1
> Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
> Context: system_u:object_r:cifs_t:s0
> Access: 2014-07-21 14:19:30.596249500 -0500
> Modify: 2014-07-21 14:20:20.157755800 -0500
> Change: 2014-07-21 14:20:20.157755800 -0500
>  Birth: -
>
> (I will send jra the wireshark trace).
>
> On Mon, Jul 21, 2014 at 1:55 PM, Jeremy Allison <jra at samba.org> wrote:
>> On Mon, Jul 21, 2014 at 01:43:12PM -0500, Steve French wrote:
>>> What about shrinking the file to the wrong size?
>>
>> In the set allocation path info it's going through:
>>
>>         if (allocation_size) {
>>                 allocation_size = smb_roundup(conn, allocation_size);
>>         }
>>
>> which by default uses 1MB allocation roundup values.
>>
>> If you need to set the file length, set the file length :-).
>>
>> It's arguable if the server can mess with allocation
>> requests on file shrink, but this hasn't caused a
>> problem in the SMB1/Windows SMB2 code paths so far,
>> so I'm guessing it might be allowable....
>>
>> More research needed !
>
>
>
> --
> Thanks,
>
> Steve



-- 
Thanks,

Steve