Re: [PATCH] ceph: fix ceph_dir_llseek()

[Alex Elder <elder@ieee.org>]

On 02/27/2014 03:07 AM, Yan, Zheng wrote:
> Comparing offset with inode->i_sb->s_maxbytes doesn't make sense for
> directory. For a fragmented directory, offset (frag_t, off) can be
> larger than inode->i_sb->s_maxbytes.
> 
> At the very beginning of ceph_dir_llseek(), local variable old_offset
> is initialized to parameter offset. This doesn't make sense neither.
> Old_offset should be ceph_make_fpos(fi->frag, fi->next_offset).

This looks OK to me, but I'm not as well-versed in the file system
code as I am in libceph and rbd.  It looks like previously this
would produce problems if you ever did an llseek on a directory
that ended up in any fragment but the first.

I have one question/suggestion below, but otherwise:

Reviewed-by: Alex Elder <elder@linaro.org>

> 
> Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
> ---
>  fs/ceph/dir.c   | 12 ++++++------
>  fs/ceph/super.h |  2 +-
>  2 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
> index 45eda6d..a7eaf96 100644
> --- a/fs/ceph/dir.c
> +++ b/fs/ceph/dir.c
> @@ -190,7 +190,7 @@ more:
>  		if (last) {
>  			/* remember our position */
>  			fi->dentry = last;
> -			fi->next_offset = di->offset;
> +			fi->next_offset = fpos_off(di->offset);
>  		}
>  		dput(dentry);
>  		return 0;
> @@ -369,9 +369,9 @@ more:
>  				fi->next_offset = 0;
>  			off = fi->next_offset;
>  		}
> +		fi->frag = frag;
>  		fi->offset = fi->next_offset;
>  		fi->last_readdir = req;
> -		fi->frag = frag;
>  
>  		if (req->r_reply_info.dir_end) {
>  			kfree(fi->last_name);
> @@ -474,7 +474,7 @@ static loff_t ceph_dir_llseek(struct file *file, loff_t offset, int whence)
>  {
>  	struct ceph_file_info *fi = file->private_data;
>  	struct inode *inode = file->f_mapping->host;
> -	loff_t old_offset = offset;
> +	loff_t old_offset = ceph_make_fpos(fi->frag, fi->next_offset);

Should this be named "next_offset" (or maybe "current_offset")?
It doesn't seem "old" to me, though I do realize it doesn't
necessarily represent where the "next" file position will be.

>  	loff_t retval;
>  
>  	mutex_lock(&inode->i_mutex);
> @@ -491,7 +491,7 @@ static loff_t ceph_dir_llseek(struct file *file, loff_t offset, int whence)
>  		goto out;
>  	}
>  
> -	if (offset >= 0 && offset <= inode->i_sb->s_maxbytes) {
> +	if (offset >= 0) {
>  		if (offset != file->f_pos) {
>  			file->f_pos = offset;
>  			file->f_version = 0;
> @@ -504,14 +504,14 @@ static loff_t ceph_dir_llseek(struct file *file, loff_t offset, int whence)
>  		 * seek to new frag, or seek prior to current chunk.
>  		 */
>  		if (offset == 0 ||
> -		    fpos_frag(offset) != fpos_frag(old_offset) ||
> +		    fpos_frag(offset) != fi->frag ||
>  		    fpos_off(offset) < fi->offset) {
>  			dout("dir_llseek dropping %p content\n", file);
>  			reset_readdir(fi);
>  		}
>  
>  		/* bump dir_release_count if we did a forward seek */
> -		if (offset > old_offset)
> +		if (fpos_cmp(offset, old_offset) > 0)
>  			fi->dir_release_count--;
>  	}
>  out:
> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> index d8801a9..70bb183 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -577,7 +577,7 @@ struct ceph_file_info {
>  
>  	/* readdir: position within a frag */
>  	unsigned offset;       /* offset of last chunk, adjusted for . and .. */
> -	u64 next_offset;       /* offset of next chunk (last_name's + 1) */
> +	unsigned next_offset;  /* offset of next chunk (last_name's + 1) */
>  	char *last_name;       /* last entry in previous chunk */
>  	struct dentry *dentry; /* next dentry (for dcache readdir) */
>  	int dir_release_count;
>