ocfs2: Implement llseek()

ocfs2 implements its own llseek() to provide the SEEK_HOLE/SEEK_DATA
functionality.

SEEK_HOLE sets the file pointer to the start of either a hole or an unwritten
(preallocated) extent, that is greater than or equal to the supplied offset.

SEEK_DATA sets the file pointer to the start of an allocated extent (not
unwritten) that is greater than or equal to the supplied offset.

If the supplied offset is on a desired region, then the file pointer is set
to it. Offsets greater than or equal to the file size return -ENXIO.

Unwritten (preallocated) extents are considered holes because the file system
treats reads to such regions in the same way as it does to holes.

Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>

3 files changed, 151 insertions, 2 deletions

diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
index 23457b491e8c..2f5b92ef0e53 100644
--- a/fs/ocfs2/extent_map.c
+++ b/fs/ocfs2/extent_map.c
@@ -832,6 +832,102 @@ out:
         return ret;
 }
 
+int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int origin)
+{
+        struct inode *inode = file->f_mapping->host;
+        int ret;
+        unsigned int is_last = 0, is_data = 0;
+        u16 cs_bits = OCFS2_SB(inode->i_sb)->s_clustersize_bits;
+        u32 cpos, cend, clen, hole_size;
+        u64 extoff, extlen;
+        struct buffer_head *di_bh = NULL;
+        struct ocfs2_extent_rec rec;
+
+        BUG_ON(origin != SEEK_DATA && origin != SEEK_HOLE);
+
+        ret = ocfs2_inode_lock(inode, &di_bh, 0);
+        if (ret) {
+                mlog_errno(ret);
+                goto out;
+        }
+
+        down_read(&OCFS2_I(inode)->ip_alloc_sem);
+
+        if (*offset >= inode->i_size) {
+                ret = -ENXIO;
+                goto out_unlock;
+        }
+
+        if (OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) {
+                if (origin == SEEK_HOLE)
+                        *offset = inode->i_size;
+                goto out_unlock;
+        }
+
+        clen = 0;
+        cpos = *offset >> cs_bits;
+        cend = ocfs2_clusters_for_bytes(inode->i_sb, inode->i_size);
+
+        while (cpos < cend && !is_last) {
+                ret = ocfs2_get_clusters_nocache(inode, di_bh, cpos, &hole_size,
+                                                 &rec, &is_last);
+                if (ret) {
+                        mlog_errno(ret);
+                        goto out_unlock;
+                }
+
+                extoff = cpos;
+                extoff <<= cs_bits;
+
+                if (rec.e_blkno == 0ULL) {
+                        clen = hole_size;
+                        is_data = 0;
+                } else {
+                        clen = le16_to_cpu(rec.e_leaf_clusters) -
+                                (cpos - le32_to_cpu(rec.e_cpos));
+                        is_data = (rec.e_flags & OCFS2_EXT_UNWRITTEN) ?  0 : 1;
+                }
+
+                if ((!is_data && origin == SEEK_HOLE) ||
+                    (is_data && origin == SEEK_DATA)) {
+                        if (extoff > *offset)
+                                *offset = extoff;
+                        goto out_unlock;
+                }
+
+                if (!is_last)
+                        cpos += clen;
+        }
+
+        if (origin == SEEK_HOLE) {
+                extoff = cpos;
+                extoff <<= cs_bits;
+                extlen = clen;
+                extlen <<=  cs_bits;
+
+                if ((extoff + extlen) > inode->i_size)
+                        extlen = inode->i_size - extoff;
+                extoff += extlen;
+                if (extoff > *offset)
+                        *offset = extoff;
+                goto out_unlock;
+        }
+
+        ret = -ENXIO;
+
+out_unlock:
+
+        brelse(di_bh);
+
+        up_read(&OCFS2_I(inode)->ip_alloc_sem);
+
+        ocfs2_inode_unlock(inode, 0);
+out:
+        if (ret && ret != -ENXIO)
+                ret = -ENXIO;
+        return ret;
+}
+
 int ocfs2_read_virt_blocks(struct inode *inode, u64 v_block, int nr,
                            struct buffer_head *bhs[], int flags,
                            int (*validate)(struct super_block *sb,
diff --git a/fs/ocfs2/extent_map.h b/fs/ocfs2/extent_map.h
index e79d41c2c909..67ea57d2fd59 100644
--- a/fs/ocfs2/extent_map.h
+++ b/fs/ocfs2/extent_map.h
@@ -53,6 +53,8 @@ int ocfs2_extent_map_get_blocks(struct inode *inode, u64 v_blkno, u64 *p_blkno,
 int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                  u64 map_start, u64 map_len);
 
+int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int origin);
+
 int ocfs2_xattr_get_clusters(struct inode *inode, u32 v_cluster,
                              u32 *p_cluster, u32 *num_clusters,
                              struct ocfs2_extent_list *el,
diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index 0fc2bd34039d..c0f015e11c28 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2591,6 +2591,57 @@ bail:
         return ret;
 }
 
+/* Refer generic_file_llseek_unlocked() */
+static loff_t ocfs2_file_llseek(struct file *file, loff_t offset, int origin)
+{
+        struct inode *inode = file->f_mapping->host;
+        int ret = 0;
+
+        mutex_lock(&inode->i_mutex);
+
+        switch (origin) {
+        case SEEK_SET:
+                break;
+        case SEEK_END:
+                offset += inode->i_size;
+                break;
+        case SEEK_CUR:
+                if (offset == 0) {
+                        offset = file->f_pos;
+                        goto out;
+                }
+                offset += file->f_pos;
+                break;
+        case SEEK_DATA:
+        case SEEK_HOLE:
+                ret = ocfs2_seek_data_hole_offset(file, &offset, origin);
+                if (ret)
+                        goto out;
+                break;
+        default:
+                ret = -EINVAL;
+                goto out;
+        }
+
+        if (offset < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET))
+                ret = -EINVAL;
+        if (!ret && offset > inode->i_sb->s_maxbytes)
+                ret = -EINVAL;
+        if (ret)
+                goto out;
+
+        if (offset != file->f_pos) {
+                file->f_pos = offset;
+                file->f_version = 0;
+        }
+
+out:
+        mutex_unlock(&inode->i_mutex);
+        if (ret)
+                return ret;
+        return offset;
+}
+
 const struct inode_operations ocfs2_file_iops = {
         .setattr        = ocfs2_setattr,
         .getattr        = ocfs2_getattr,
@@ -2615,7 +2666,7 @@ const struct inode_operations ocfs2_special_file_iops = {
  * ocfs2_fops_no_plocks and ocfs2_dops_no_plocks!
  */
 const struct file_operations ocfs2_fops = {
-        .llseek         = generic_file_llseek,
+        .llseek         = ocfs2_file_llseek,
         .read           = do_sync_read,
         .write          = do_sync_write,
         .mmap           = ocfs2_mmap,
@@ -2663,7 +2714,7 @@ const struct file_operations ocfs2_dops = {
  * the cluster.
  */
 const struct file_operations ocfs2_fops_no_plocks = {
-        .llseek         = generic_file_llseek,
+        .llseek         = ocfs2_file_llseek,
         .read           = do_sync_read,
         .write          = do_sync_write,
         .mmap           = ocfs2_mmap,