On 04/23/2012 10:37 PM, Eric Sandeen wrote:
> On 4/22/12 7:51 AM, Bernd Schubert wrote:
>> On 04/20/2012 10:04 PM, Eric Sandeen wrote:
>>> On 1/9/12 7:21 AM, Bernd Schubert wrote:
>>>> From: Fan Yong <yong.fan@xxxxxxxxxxxxx>
>>>>
>>>> Traditionally ext2/3/4 has returned a 32-bit hash value from llseek()
>>>> to appease NFSv2, which can only handle a 32-bit cookie for seekdir()
>>>> and telldir(). However, this causes problems if there are 32-bit hash
>>>> collisions, since the NFSv2 server can get stuck resending the same
>>>> entries from the directory repeatedly.
>>>>
>>>> Allow ext4 to return a full 64-bit hash (both major and minor) for
>>>> telldir to decrease the chance of hash collisions. This still needs
>>>> integration on the NFS side.
>>>>
>>>> Patch-updated-by: Bernd Schubert <bernd.schubert@xxxxxxxxxxxxxxxxxx>
>>>> (blame me if something is not correct)
>>>
>>> Bernd, I've merged this to ext3. Bruce thought maybe you were working
>>> on the same. Should I send mine?
>>
>> That is perfectly fine with me.
>>
>>>
>>> Also...
>>>
>>>> +/*
>>>> + * ext4_dir_llseek() based on generic_file_llseek() to handle both
>>>> + * non-htree and htree directories, where the "offset" is in terms
>>>> + * of the filename hash value instead of the byte offset.
>>>> + *
>>>> + * NOTE: offsets obtained *before* ext4_set_inode_flag(dir, EXT4_INODE_INDEX)
>>>> + * will be invalid once the directory was converted into a dx directory
>>>> + */
>>>> +loff_t ext4_dir_llseek(struct file *file, loff_t offset, int origin)
>>>
>>> ext4_llseek() worries about max offset for direct/indirect vs. extent-mapped
>>> files. Do we need to worry about the same thing in this function?
>>
>> Hrmm, I just checked it and I think either is wrong. We only have to
>> care about non-dx directories, so ext4_readdir() applies, which limits
>> filp->f_pos < inode->i_size.
>> Going to send a patch tomorrow. Thanks for spotting this!
>
> The other thing I'm wondering is whether, in light of
>
> ef3d0fd27e90f67e35da516dafc1482c82939a60 vfs: do (nearly) lockless generic_file_llseek
>
> taking the i_mutex in ext4_dir_llseek could be a perf regression vs what was there before? Is there anything about the new function which requires stronger locking?
>
> I may be missing something obvious about the nfs interaction, not sure.
>
Oh, good point. I was just about to send a small patch, but reading
through the lockless commit will take some time - its already too late
for me for today. Will work on that tomorrow. Thanks again for your review!
Cheers,
Bernd
diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index b867862..3a4988e2 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -363,7 +363,7 @@ loff_t ext4_dir_llseek(struct file *file, loff_t
offset, int origin)
goto out_err;
if (!dx_dir) {
- if (offset > inode->i_sb->s_maxbytes)
+ if (offset > i_size_read(inode))
goto out_err;
} else if (offset > ext4_get_htree_eof(file))
goto out_err;
--
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