linux-kernel - Re: [PATCH 1/7] BTRFS: Fix lseek return value for error

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Date:	Sun, 18 Sep 2011 15:29:41 +0800
From:	Jeff Liu <jeff.liu@...cle.com>
To:	Andi Kleen <ak@...ux.intel.com>, Andreas Dilger <adilger@...ger.ca>
CC:	Christoph Hellwig <hch@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH 1/7] BTRFS: Fix lseek return value for error

Hi Andreas and Andi,

Thanks for your comments.

On 09/18/2011 09:46 AM, Andi Kleen wrote:

>>> with an additional improvement if the offset is larger or equal to the
>>> file size, return -ENXIO in directly:
>>>
>>>                if (offset >= inode->i_size) {
>>>                        mutex_unlock(&inode->i_mutex);
>>>                        return -ENXIO;
>>>                }
>>
>> Except that is wrong, because it would then be impossible to write sparse files. 

Per my tryout, except that, if the offset >= source file size, call
lseek(fd, offset, SEEK_DATA/SEEK_HOLE) against Btrfs will always return
the total file size rather than -ENXIO.  however, our desired result it
-ENXIO in this case, Am I right?

> 
> And also i_size must be always read with i_size_read()

Thanks for pointing this out!
Would you please kindly review the revised as below?

Signed-off-by: Jie Liu <jeff.liu@...cle.com>

---
 fs/btrfs/file.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index e7872e4..40c1ef3 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1813,6 +1813,11 @@ static loff_t btrfs_file_llseek(struct file
*file, loff_t offset, int origin)
 		goto out;
 	case SEEK_DATA:
 	case SEEK_HOLE:
+		if (offset >= i_size_read(inode)) {
+			mutex_unlock(&inode->i_mutex);
+			return -ENXIO;
+		}
+
 		ret = find_desired_extent(inode, &offset, origin);
 		if (ret) {
 			mutex_unlock(&inode->i_mutex);
@@ -1821,11 +1826,11 @@ static loff_t btrfs_file_llseek(struct file
*file, loff_t offset, int origin)
 	}

 	if (offset < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET)) {
-		ret = -EINVAL;
+		offset = -EINVAL;
 		goto out;
 	}
 	if (offset > inode->i_sb->s_maxbytes) {
-		ret = -EINVAL;
+		offset = -EINVAL;
 		goto out;
 	}

-- 
1.7.4.1
--
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