[PATCH 4/4] gfs2: Implement lseek SEEK_HOLE / SEEK_DATA via iomap

[Andreas Gruenbacher <agruenba@redhat.com>]

Add a vfs helper for implementing lseek SEEK_HOLE / SEEK_DATA support
via iomap.  Wire up in gfs2.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 fs/gfs2/file.c        | 14 ++++++++++---
 fs/gfs2/inode.c       | 32 ++++++++++++++++++++++++++++++
 fs/gfs2/inode.h       |  1 +
 fs/iomap.c            | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/iomap.h |  2 ++
 5 files changed, 101 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index c2062a1..62ce320 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -60,9 +60,7 @@ static loff_t gfs2_llseek(struct file *file, loff_t offset, int whence)
 	loff_t error;
 
 	switch (whence) {
-	case SEEK_END: /* These reference inode->i_size */
-	case SEEK_DATA:
-	case SEEK_HOLE:
+	case SEEK_END:
 		error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY,
 					   &i_gh);
 		if (!error) {
@@ -70,8 +68,18 @@ static loff_t gfs2_llseek(struct file *file, loff_t offset, int whence)
 			gfs2_glock_dq_uninit(&i_gh);
 		}
 		break;
+
+	case SEEK_DATA:
+	case SEEK_HOLE:
+		error = gfs2_seek_hole_data(file, offset, whence);
+		break;
+
 	case SEEK_CUR:
 	case SEEK_SET:
+		/*
+		 * These don't reference inode->i_size and don't depend on the
+		 * block mapping, so we don't need the glock.
+		 */
 		error = generic_file_llseek(file, offset, whence);
 		break;
 	default:
diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index 9ed2e91..f3bf740 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -2046,6 +2046,38 @@ static int gfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	return ret;
 }
 
+loff_t gfs2_seek_hole_data(struct file *file, loff_t offset, int whence)
+{
+	struct inode *inode = file->f_mapping->host;
+	struct gfs2_inode *ip = GFS2_I(inode);
+	struct gfs2_holder gh;
+	loff_t ret;
+
+	inode_lock(inode);
+	ret = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
+	if (ret)
+		goto out;
+	if (gfs2_is_stuffed(ip)) {
+		u64 size = i_size_read(inode);
+
+		if (offset >= size) {
+			ret = -ENXIO;
+			goto out_dequeue;
+		}
+		ret = offset;
+		if (whence == SEEK_HOLE)
+			ret = size;
+	} else {
+		ret = iomap_seek_hole_data(inode, offset, whence, &gfs2_iomap_ops);
+	}
+
+out_dequeue:
+	gfs2_glock_dq_uninit(&gh);
+out:
+	inode_unlock(inode);
+	return ret;
+}
+
 const struct inode_operations gfs2_file_iops = {
 	.permission = gfs2_permission,
 	.setattr = gfs2_setattr,
diff --git a/fs/gfs2/inode.h b/fs/gfs2/inode.h
index aace8ce..9e64b05 100644
--- a/fs/gfs2/inode.h
+++ b/fs/gfs2/inode.h
@@ -109,6 +109,7 @@ extern int gfs2_setattr_simple(struct inode *inode, struct iattr *attr);
 extern struct inode *gfs2_lookup_simple(struct inode *dip, const char *name);
 extern void gfs2_dinode_out(const struct gfs2_inode *ip, void *buf);
 extern int gfs2_open_common(struct inode *inode, struct file *file);
+extern loff_t gfs2_seek_hole_data(struct file *file, loff_t pos, int whence);
 
 extern const struct inode_operations gfs2_file_iops;
 extern const struct inode_operations gfs2_dir_iops;
diff --git a/fs/iomap.c b/fs/iomap.c
index 4b10892..59350ef 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -584,6 +584,61 @@ int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fi,
 }
 EXPORT_SYMBOL_GPL(iomap_fiemap);
 
+static loff_t
+iomap_seek_hole_actor(struct inode *inode, loff_t offset, loff_t length,
+		      void *data, struct iomap *iomap)
+{
+	if (iomap->type == IOMAP_HOLE)
+		return 0;
+	return iomap->offset + iomap->length - offset;
+}
+
+static loff_t
+iomap_seek_data_actor(struct inode *inode, loff_t offset, loff_t length,
+		      void *data, struct iomap *iomap)
+{
+	if (iomap->type != IOMAP_HOLE)
+		return 0;
+	return iomap->offset + iomap->length - offset;
+}
+
+loff_t
+iomap_seek_hole_data(struct inode *inode, loff_t offset, int whence,
+		     const struct iomap_ops *ops)
+{
+	static loff_t (*actor)(struct inode *, loff_t, loff_t, void *, struct iomap *);
+	loff_t len = i_size_read(inode) - offset;
+	loff_t ret;
+
+	if (len <= 0)
+		return -ENXIO;
+
+	switch(whence) {
+	case SEEK_HOLE:
+		actor = iomap_seek_hole_actor;
+		break;
+
+	case SEEK_DATA:
+		actor = iomap_seek_data_actor;
+		break;
+	}
+
+	while (len > 0) {
+		ret = iomap_apply(inode, offset, len, IOMAP_REPORT, ops, NULL, actor);
+		if (ret <= 0)
+			break;
+		offset += ret;
+		len -= ret;
+	}
+	if (ret < 0)
+		return ret;
+	ret = offset;
+	if (len <= 0 && whence == SEEK_DATA)
+		ret = -ENXIO;
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iomap_seek_hole_data);
+
 /*
  * Private flags for iomap_dio, must not overlap with the public ones in
  * iomap.h:
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 9d64933..63bd998 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -84,6 +84,8 @@ int iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
 int iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops);
 int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		loff_t start, loff_t len, const struct iomap_ops *ops);
+loff_t iomap_seek_hole_data(struct inode *inode, loff_t pos, int whence,
+			    const struct iomap_ops *ops);
 
 /*
  * Flags for direct I/O ->end_io:
-- 
2.7.4