Re: [PATCH 04/12] xfs: handle unallocated inodes in xfs_inode_from_disk

[Brian Foster <bfoster@redhat.com>]

On Fri, May 01, 2020 at 10:14:16AM +0200, Christoph Hellwig wrote:
> Handle inodes with a 0 di_mode in xfs_inode_from_disk, instead of partially
> duplicating inode reading in xfs_iread.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_inode_buf.c | 54 ++++++++++++-----------------------
>  1 file changed, 18 insertions(+), 36 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> index 983beb680e81a..b136f29f7d9d3 100644
> --- a/fs/xfs/libxfs/xfs_inode_buf.c
> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> @@ -198,6 +198,21 @@ xfs_inode_from_disk(
>  	ASSERT(ip->i_cowfp == NULL);
>  	ASSERT(ip->i_afp == NULL);
>  
> +	/*
> +	 * Get the truly permanent information first that is not overwritten by
> +	 * xfs_ialloc first.  This also includes i_mode so that a newly read
> +	 * in inode structure for an allocation is marked as already free.
> +	 */

The first sentence has a wording issue and the second is kind of
confusing. I think this can be simplified and condensed further (see the
diff below for example). Otherwise looks good.

Brian

diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
index b136f29f7d9d..ed02649138aa 100644
--- a/fs/xfs/libxfs/xfs_inode_buf.c
+++ b/fs/xfs/libxfs/xfs_inode_buf.c
@@ -199,17 +199,14 @@ xfs_inode_from_disk(
 	ASSERT(ip->i_afp == NULL);
 
 	/*
-	 * Get the truly permanent information first that is not overwritten by
-	 * xfs_ialloc first.  This also includes i_mode so that a newly read
-	 * in inode structure for an allocation is marked as already free.
+	 * First get the permanent information that is needed to allocate an
+	 * inode. If the inode is unused, mode is zero and we shouldn't mess
+	 * with the unitialized part of it.
 	 */
+	to->di_flushiter = be16_to_cpu(from->di_flushiter);
 	inode->i_generation = be32_to_cpu(from->di_gen);
 	inode->i_mode = be16_to_cpu(from->di_mode);
-	to->di_flushiter = be16_to_cpu(from->di_flushiter);
 
-	/*
-	 * Only copy the rest if the inode is actually allocated.
-	 */
 	if (!inode->i_mode)
 		return 0;
 

> +	inode->i_generation = be32_to_cpu(from->di_gen);
> +	inode->i_mode = be16_to_cpu(from->di_mode);
> +	to->di_flushiter = be16_to_cpu(from->di_flushiter);
> +
> +	/*
> +	 * Only copy the rest if the inode is actually allocated.
> +	 */
> +	if (!inode->i_mode)
> +		return 0;
> +
>  	/*
>  	 * Convert v1 inodes immediately to v2 inode format as this is the
>  	 * minimum inode version format we support in the rest of the code.
> @@ -215,7 +230,6 @@ xfs_inode_from_disk(
>  	to->di_format = from->di_format;
>  	i_uid_write(inode, be32_to_cpu(from->di_uid));
>  	i_gid_write(inode, be32_to_cpu(from->di_gid));
> -	to->di_flushiter = be16_to_cpu(from->di_flushiter);
>  
>  	/*
>  	 * Time is signed, so need to convert to signed 32 bit before
> @@ -229,8 +243,6 @@ xfs_inode_from_disk(
>  	inode->i_mtime.tv_nsec = (int)be32_to_cpu(from->di_mtime.t_nsec);
>  	inode->i_ctime.tv_sec = (int)be32_to_cpu(from->di_ctime.t_sec);
>  	inode->i_ctime.tv_nsec = (int)be32_to_cpu(from->di_ctime.t_nsec);
> -	inode->i_generation = be32_to_cpu(from->di_gen);
> -	inode->i_mode = be16_to_cpu(from->di_mode);
>  
>  	to->di_size = be64_to_cpu(from->di_size);
>  	to->di_nblocks = be64_to_cpu(from->di_nblocks);
> @@ -659,39 +671,9 @@ xfs_iread(
>  		goto out_brelse;
>  	}
>  
> -	/*
> -	 * If the on-disk inode is already linked to a directory
> -	 * entry, copy all of the inode into the in-core inode.
> -	 * xfs_iformat_fork() handles copying in the inode format
> -	 * specific information.
> -	 * Otherwise, just get the truly permanent information.
> -	 */
> -	if (dip->di_mode) {
> -		error = xfs_inode_from_disk(ip, dip);
> -		if (error)  {
> -#ifdef DEBUG
> -			xfs_alert(mp, "%s: xfs_iformat() returned error %d",
> -				__func__, error);
> -#endif /* DEBUG */
> -			goto out_brelse;
> -		}
> -	} else {
> -		/*
> -		 * Partial initialisation of the in-core inode. Just the bits
> -		 * that xfs_ialloc won't overwrite or relies on being correct.
> -		 */
> -		VFS_I(ip)->i_generation = be32_to_cpu(dip->di_gen);
> -		ip->i_d.di_flushiter = be16_to_cpu(dip->di_flushiter);
> -
> -		/*
> -		 * Make sure to pull in the mode here as well in
> -		 * case the inode is released without being used.
> -		 * This ensures that xfs_inactive() will see that
> -		 * the inode is already free and not try to mess
> -		 * with the uninitialized part of it.
> -		 */
> -		VFS_I(ip)->i_mode = 0;
> -	}
> +	error = xfs_inode_from_disk(ip, dip);
> +	if (error)
> +		goto out_brelse;
>  
>  	ip->i_delayed_blks = 0;
>  
> -- 
> 2.26.2
>