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Re: [PATCH] xfs: clean up xfs_set_maxicount & use in growfs

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: clean up xfs_set_maxicount & use in growfs
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Wed, 26 Feb 2014 12:29:22 -0600
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140226021114.GA26022@xxxxxxxxxxxxx>
References: <530C29C7.90001@xxxxxxxxxx> <20140226021114.GA26022@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.3.0
On 2/25/14, 8:11 PM, Christoph Hellwig wrote:
> On Mon, Feb 24, 2014 at 11:27:35PM -0600, Eric Sandeen wrote:
>> xfs_set_maxicount() overflowed fairly easily for large filesystems
>> and large maxicount; we started out by multiplying dblocks by
>> the percentage, *then* dividing by 100, and never checked for
>> an overflow.  The calculations were also, IMHO, a little hard
>> to follow.
> 
> Would be useful to get this test case into xfstests..

Ok so I was going on Dave's assertion about that.  ;)

To overflow, we'd need dblocks * 100 to be > 2^64-1:

so dblocks would need to be > (2^64-1)/100

for 4k blocks that's 655 exabytes.  Maybe not so possible after all ;)

Dave, maybe just removing the open-code is enough here.

-Eric

>> -STATIC void
>> +void
>>  xfs_set_maxicount(xfs_mount_t *mp)
>>  {
>>      xfs_sb_t        *sbp = &(mp->m_sb);
>> -    __uint64_t      icount;
>> +    __uint64_t      iblocks;
> 
> Seems like this could move into the if clause below.
> 
>> @@ -388,6 +388,7 @@ extern int       xfs_mod_incore_sb_batch(xfs_mount_t *, 
>> xfs_mod_sb_t *,
>>  extern int  xfs_mount_log_sb(xfs_mount_t *, __int64_t);
>>  extern struct xfs_buf *xfs_getsb(xfs_mount_t *, int);
>>  extern int  xfs_readsb(xfs_mount_t *, int);
>> +void                xfs_set_maxicount(xfs_mount_t *mp);
>>  extern void xfs_freesb(xfs_mount_t *);
>>  extern int  xfs_fs_writable(xfs_mount_t *);
>>  extern int  xfs_sb_validate_fsb_count(struct xfs_sb *, __uint64_t);
> 
> A missing extern while all other prototypes around it have one seems
> rather odd.
> 
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