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Subject: Re: posix_fallocate on ZFS
To: Ian Lepore <ian@freebsd.org>, Alan Somers <asomers@freebsd.org>
Cc: freebsd current <freebsd-current@freebsd.org>
References: <1e2f43fd-85da-6629-62d1-6e96790278e5@digiware.nl>
 <CAOtMX2jZr_kvJgOZWeiB-AZ3-7-uUu+UQ3P0nKhGZ0eNRzwMOQ@mail.gmail.com>
 <1518291799.32585.228.camel@freebsd.org>
From: Willem Jan Withagen <wjw@digiware.nl>
Message-ID: <4fa8de06-c7a0-5585-4fa7-5bf59b99d627@digiware.nl>
Date: Sat, 10 Feb 2018 23:50:01 +0100
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On 10/02/2018 20:43, Ian Lepore wrote:
> On Sat, 2018-02-10 at 11:24 -0700, Alan Somers wrote:
>> On Sat, Feb 10, 2018 at 10:28 AM, Willem Jan Withagen
>> wrote:
>>
>>>
>>> Hi,
>>>
>>> This has been disabled on ZFS since last November.
>>> And I do understand the rationale on this.
>>>
>>> BUT
>>>
>>> I've now upgraded some of my HEAD Ceph test systems and they now fail,
>>> since Ceph uses posix_fallocate() to allocate space for the
>>> FileStore-journal.
>>>
>>> Is there any expectation that this is going to fixed in any near future?
>>>
>>> --WjW
>>>
>> No.  It's fundamentally impossible to support posix_fallocate on a COW
>> filesystem like ZFS.  Ceph should be taught to ignore an EINVAL result,
>> since the system call is merely advisory.
>>
>> -Alan
> 
> Unfortunately, posix documents that the function returns EINVAL only
> due to bad input parameters, so ignoring that seems like a bad idea.
> 
> Wouldn't it be better if we returned EOPNOTSUP if that's the actual
> situation?  That could be safely ignored.

I would probably help in my situation....

And I've been looking at the manpage, but cannot seem to find any 
indication that EINVAL is returned on running it on FreeBSD.

--WjW