linux-kernel - Re: [PATCH] Add support to check for FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_ZERO

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Message-ID: <CAPDOMVj8cEsgR1TTOkTUWaxMHiEbpnM6qcj7opRuRLP+3YOfTg@mail.gmail.com>
Date:	Thu, 31 Jul 2014 21:53:15 -0400
From:	Nick Krause <xerofoify@...il.com>
To:	Hugo Mills <hugo@...fax.org.uk>,
	Nicholas Krause <xerofoify@...il.com>,
	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	"linux-btrfs@...r.kernel.org SYSTEM list:BTRFS FILE" 
	<linux-btrfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add support to check for FALLOC_FL_COLLAPSE_RANGE and
 FALLOC_FL_ZERO_RANGE crap modes

On Thu, Jul 31, 2014 at 3:09 PM, Hugo Mills <hugo@...fax.org.uk> wrote:
> On Thu, Jul 31, 2014 at 01:53:33PM -0400, Nicholas Krause wrote:
>> This adds checks for the stated modes as if they are crap we will return error
>> not supported.
>
>    You've just enabled two options, but you haven't actually
> implemented the code behind it. I would tell you *NOT* to do anything
> else on this work until you can answer the question: What happens if
> you apply this patch, create a large file called "foo.txt", and then a
> userspace program executes the following code?
>
> int fd = open("foo.txt", O_RDWR);
> fallocate(fd, FALLOCATE_FL_COLLAPSE_RANGE, 50, 50);
>
>    Try it on a btrfs filesystem, both with and without your patch.
> Also try it on an ext4 filesystem.
>
>    Once you've done all of that, reply to this mail and tell me what
> the problem is with this patch. You need to make two answers: what are
> the technical problems with the patch? What errors have you made in
> the development process?
>
>    *Only* if you can answer those questions sensibly, should you write
> any more patches, of any kind.
>
>    Hugo.
>
>> Signed-off-by: Nicholas Krause <xerofoify@...il.com>
>> ---
>>  fs/btrfs/file.c |    3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
>> index 1f2b99c..599495a 100644
>> --- a/fs/btrfs/file.c
>> +++ b/fs/btrfs/file.c
>> @@ -2490,7 +2490,8 @@ static long btrfs_fallocate(struct file *file, int mode,
>>       alloc_end = round_up(offset + len, blocksize);
>>
>>       /* Make sure we aren't being give some crap mode */
>> -     if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
>> +     if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE|
>> +     FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE))
>>               return -EOPNOTSUPP;
>>
>>       if (mode & FALLOC_FL_PUNCH_HOLE)
>> --
>> 1.7.10.4
>>
>> --
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>
> --
> === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
>   PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk
>   --- The glass is neither half-full nor half-empty; it is twice as ---
>                         large as it needs to be.
Calls are there in btrfs , therefore will either kernel panic or cause an oops.
Need to test this patch as this is very easy to catch bug.
Nick
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