Re: [PATCH v3 4/5] fat (exportfs): rebuild directory-inode if fat_dget() fails

[OGAWA Hirofumi]

Namjae Jeon <linkinjeon@xxxxxxxxx> writes:

> From: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
>
> This patch enables rebuilding of directory inodes which are not present
> in the cache.This is done by traversing the disk clusters to find the
> directory entry of the parent directory and using its i_pos to build the
> inode.

Hmm... Is this functionality is necessary to work correctly? If we
didn't provide this, which case do server return ESTALE?

Well, this looks like duplication of lookup, we may need to consolidate.

> Signed-off-by: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
> Signed-off-by: Ravishankar N <ravi.n1@xxxxxxxxxxx>
> Signed-off-by: Amit Sahrawat <a.sahrawat@xxxxxxxxxxx>
> ---
>  fs/fat/nfs.c |  132 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 128 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fat/nfs.c b/fs/fat/nfs.c
> index 3cf5412..bb4262c 100644
> --- a/fs/fat/nfs.c
> +++ b/fs/fat/nfs.c
> @@ -104,6 +104,93 @@ struct dentry *fat_fh_to_parent(struct super_block *sb, struct fid *fid,
>  }
>  
>  /*
> + * Read the directory entries of 'search_clus' and find the entry
> + * which contains 'match_ipos' for the starting cluster.If the entry
> + * is found, rebuild its inode.
> + */
> +static struct inode *fat_traverse_cluster(struct super_block *sb,
> +				int search_clus, int match_ipos)
> +{
> +	struct msdos_sb_info *sbi = MSDOS_SB(sb);
> +	struct buffer_head *bh;
> +	sector_t blknr;
> +	int parent_ipos, search_ipos;
> +	int i;
> +	struct msdos_dir_entry *de;
> +	struct inode *inode = NULL;
> +	int iterations = sbi->cluster_size >> sb->s_blocksize_bits;
> +	blknr = fat_clus_to_blknr(sbi, search_clus);
> +
> +	do {
> +		bh = sb_bread(sb, blknr);
> +		if (!bh) {
> +			fat_msg(sb, KERN_ERR,
> +				 "NFS:unable to read block(%llu) while traversing cluster(%d)",
> +				(llu)blknr, search_clus);
> +			inode = ERR_PTR(-EIO);
> +			goto out;
> +		}
> +		de = (struct msdos_dir_entry *)bh->b_data;
> +		for (i = 0; i < sbi->dir_per_block; i++) {
> +			if (de[i].name[0] == FAT_ENT_FREE) {
> +				/*Reached end of directory*/
> +				brelse(bh);
> +				inode = ERR_PTR(-ENODATA);
> +				goto out;
> +			}
> +			if (de[i].name[0] == DELETED_FLAG)
> +				continue;
> +			if (de[i].attr == ATTR_EXT)
> +				continue;
> +			if (!(de[i].attr & ATTR_DIR))
> +				continue;
> +			else {
> +				search_ipos = fat_get_start(sbi, &de[i]);
> +				if (search_ipos == match_ipos) {
> +					/*Success.Now build the inode*/
> +					parent_ipos = (loff_t)i +
> +					 (blknr << sbi->dir_per_block_bits);
> +					inode = fat_build_inode(sb, &de[i],
> +								parent_ipos);
> +					brelse(bh);
> +					goto out;
> +				}
> +			}
> +		}
> +		brelse(bh);
> +		blknr += 1;
> +	} while (--iterations > 0);
> +out:
> +	return inode;
> +}
> +
> +/*
> + * Read the FAT to find the next cluster in the chain
> + * corresponding to 'search_clus'.
> + */
> +static int fat_read_next_clus(struct super_block *sb, int search_clus)
> +{
> +	struct msdos_sb_info *sbi = MSDOS_SB(sb);
> +	/*bits 31 to 7 give relative sector number*/
> +	sector_t blknr = search_clus >> 7;
> +	/*bits 6 to 0 give offset*/
> +	unsigned int offset = search_clus & 0x7F;
> +	__le32 *address;
> +	unsigned int next_cluster;
> +	struct buffer_head *bh = sb_bread(sb, blknr + sbi->fat_start);
> +	if (!bh) {
> +		fat_msg(sb, KERN_ERR,
> +			"NFS:unable to read block(%llu) for finding the next cluster in FAT chain",
> +			(llu)blknr);
> +		return -EIO;
> +	}
> +	address = (__le32 *) bh->b_data;
> +	next_cluster = (le32_to_cpu(address[offset])) & 0x0FFFFFFF;
> +	brelse(bh);
> +	return next_cluster;
> +}
> +
> +/*
>   * Find the parent for a directory that is not currently connected to
>   * the filesystem root.
>   *
> @@ -112,15 +199,52 @@ struct dentry *fat_fh_to_parent(struct super_block *sb, struct fid *fid,
>  struct dentry *fat_get_parent(struct dentry *child_dir)
>  {
>  	struct super_block *sb = child_dir->d_sb;
> -	struct buffer_head *bh = NULL;
> +	struct buffer_head *dotdot_bh = NULL, *parent_bh = NULL;
>  	struct msdos_dir_entry *de;
>  	struct inode *parent_inode = NULL;
> +	struct msdos_sb_info *sbi = MSDOS_SB(sb);
> +	int parent_logstart;
> +	int search_clus, clus_to_match;
> +	sector_t blknr;
>  
> -	if (!fat_get_dotdot_entry(child_dir->d_inode, &bh, &de)) {
> -		int parent_logstart = fat_get_start(MSDOS_SB(sb), de);
> +	if (!fat_get_dotdot_entry(child_dir->d_inode, &dotdot_bh, &de)) {
> +		parent_logstart = fat_get_start(sbi, de);
>  		parent_inode = fat_dget(sb, parent_logstart);
> +		if (parent_inode || sbi->options.nfs != FAT_NFS_LIMITED)
> +			goto out;
> +		if (!parent_logstart)
> +			/*logstart of dotdot entry is zero if
> +			* if the directory's parent is root
> +			*/
> +			parent_inode = sb->s_root->d_inode;
> +		else {
> +			blknr = fat_clus_to_blknr(sbi, parent_logstart);
> +			parent_bh = sb_bread(sb, blknr);
> +			if (!parent_bh) {
> +				fat_msg(sb, KERN_ERR,
> +					"NFS:unable to read cluster of parent directory");
> +				goto out;
> +			}
> +			de = (struct msdos_dir_entry *) parent_bh->b_data;
> +			clus_to_match = fat_get_start(sbi, &de[0]);
> +			search_clus = fat_get_start(sbi, &de[1]);
> +			if (!search_clus)
> +				search_clus = sbi->root_cluster;
> +			brelse(parent_bh);
> +			do {
> +				parent_inode =  fat_traverse_cluster(sb,
> +						search_clus, clus_to_match);
> +				if (IS_ERR(parent_inode) || parent_inode)
> +					break;
> +				search_clus = fat_read_next_clus(sb,
> +								search_clus);
> +				if (search_clus < 0)
> +					break;
> +			} while (search_clus != FAT_ENT_EOF);
> +		}
>  	}
> -	brelse(bh);
> +out:
> +	brelse(dotdot_bh);
>  
>  	return d_obtain_alias(parent_inode);
>  }

-- 
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
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