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Subject: Re: Using fstatfs on a ZFS disk
To: Andriy Gapon <avg@FreeBSD.org>,
 "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net>, rb@gid.co.uk
Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>
References: <456B0CAA-367F-478A-BB61-153942C3EB7A@gid.co.uk>
 <201802191833.w1JIXhVL078022@pdx.rh.CN85.dnsmgr.net>
 <45bd4a05-406b-d6ac-6679-6897ab1fc742@FreeBSD.org>
From: Willem Jan Withagen <wjw@digiware.nl>
Message-ID: <8134dba0-fdae-0109-4bae-3441d750566d@digiware.nl>
Date: Mon, 19 Feb 2018 23:03:19 +0100
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On 19-2-2018 22:20, Andriy Gapon wrote:
> On 19/02/2018 20:33, Rodney W. Grimes wrote:
>>> Hi,
>>>
>>>> On 19 Feb 2018, at 15:50, Willem Jan Withagen <wjw@digiware.nl> wrote:
> 
>>>> 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.
> 
> This is simpler, I think.
> It is a hash value (calculated using a specific algorithm) of a filesystem type
> name.  See vfs_register().

Right in vfs_init.c

> There are no magic predefined constants for the types.

It is a bit of work doing the hashes, but there could very well be 
pre-calculated FS_<fs>_TYPE defines.

See my other post.

> BTW, lsvfs(1) and its source code could be of interest to the original poster.
> E.g., getvfsbyname(3).

lsvfs output could even be used to generate part of the ENUM list.

--WjW