Using fstatfs on a ZFS disk

[Willem Jan Withagen]

On 19/02/2018 19:33, Rodney W. Grimes wrote:
>> Hi,
>>
>>> On 19 Feb 2018, at 15:50, Willem Jan Withagen <wjw at digiware.nl> wrote:
>>>
>>> On 19-2-2018 16:00, Bob Bishop wrote:
>>>> Hi,
>>>>> On 19 Feb 2018, at 14:48, Willem Jan Withagen <wjw at digiware.nl> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I'm trying to find the values of the returned f_type for ZFS
>>>>> in the fstatfs call when a file is on ZFS....
>>>>>
>>>>> But I have not yet found the definitions of the ENUMS that
>>>>> would fill that value... Let alone the value for ZFS.
>>>> I chased this particular wild goose myself recently. It?s FS_... in  /usr/include/sys/disklabel,h that you want.
>>>
>>> Hi Bob,
>>>
>>> I grepped on MAGIC and FS, but the combo did not deliver anything useful. So this is already more that I found.
>>> I did get:
>>> /usr/include/ufs/ffs/fs.h:#define       FS_UFS1_MAGIC   0x011954 /* UFS1 fast filesystem magic number */
>>> /usr/include/ufs/ffs/fs.h:#define       FS_UFS2_MAGIC   0x19540119 /* UFS2 fast filesystem magic number */
>>> /usr/include/ufs/ffs/fs.h:#define       FS_BAD_MAGIC    0x19960408 /* UFS incomplete newfs magic number */
>>
>> Those I believe are magic numbers for UFS superblocks...
>>
>>> So I was looking for something like: FS_ZFS_MAGIC
>>
>> ... so you won?t find that.
>>
>>> disklabel.h contains:
>>> #ifdef  FSTYPENAMES
>>> static const char *fstypenames[] = {
>>>
>>> And further search:
>>> /usr/include/sys/disk/bsd.h:#define     FS_ZFS  27    /* Sun's ZFS */
>>>
>>> Running:
>>> #include "stdio.h"
>>>
>>> #include <sys/param.h>
>>> #include <sys/mount.h>
>>>
>>> int main() {
>>>         struct statfs fstr;
>>>         char * str;
>>>
>>>         str = "/tmp";
>>>         statfs(str, &fstr);
>>>         printf("%s, ftype: 0x%x.\n", str, fstr.f_type);
>>> }
>>> results in:
>>> 	/tmp, ftype: 0xde.
>>>
>>> Now 0xde != 27, so the question is, where is this 0xde specified.
>>> And more important is this f_type constant over all FreeBSD ZFS filesystems?
>>
>> You got me. And a quick look at sys/kern/vfs_syscalls.c doesn?t help except to imply that the type is set when the filesystem is mounted. I have no idea where 0xde comes from.
> 
> Could that 0xde be the start of 0xdeadcode?
> 
> 0xde is 222 decimal, that does not ring a bell for me either.

Searching on 0xde did deliver indeed plenty 0xdeadc0de and sisters.
the resulting size is 32bit, so if it is a leftover of 0xdeadcode, it is 
due to a not-32bit aligned access, since the 3 upper bytes are 0.

Only way to find this out is dig thru the code. :) But I'm no hero at that.

But there is atleast not a particular FS_ZFS_MAGIC!!
And there is no obvious definition what is returned in f_type??

--WjW

>>>>>      struct statfs {
>>>>>      uint32_t f_version;             /* structure version number */
>>>>>      uint32_t f_type;                /* type of filesystem */
>>>>>      uint64_t f_flags;               /* copy of mount exported flags */
>>>>>      ......
>>>>>      }
>>>>>
>>>>> Any hints where to look would be welcomed.
>>>>>
>>>>> Thanx,
>>>>> --WjW
>>>> --
>>>> Bob Bishop
>>>> rb at gid.co.uk
>> --
>> Bob Bishop       t: +44 (0)118 940 1243
>> rb at gid.co.uk     m: +44 (0)783 626 4518
>