[PATCH] btrfs: add new ioctl to determine size of compressed file

[David Sterba <dsterba@suse.cz>]

Go through all extents of a file in a given [start,end) range and sum
for:
* regular extent: ->block_len, size is already rounded up to blocks
* inline extents: length rounded up to 512

The range is start inclusive / end exclusive. For the whole file pass
0 and (u64)-1.

The resulting value is number of occupied 512B sectors so this can
be easily compared to stat.st_blocks to determine rough compression
ratio of a file.

Based on implementation from Ulrich Hecht,
http://comments.gmane.org/gmane.comp.file-systems.btrfs/6253

Signed-off-by: David Sterba <dsterba@suse.cz>
---
 fs/btrfs/ioctl.c |   77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/ioctl.h |   11 +++++++
 2 files changed, 88 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index c04f02c..82c3810 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2972,6 +2972,81 @@ static int build_ino_list(u64 inum, u64 offset, u64 root, void *ctx)
 	return 0;
 }
 
+/*
+ * Returns the compressed size of an inode in 512 byte blocks.
+ * Count the on-disk space used by extents starting in range [start, end),
+ * inline data are rounded up to sector, ie. 512.
+ *
+ * The range is start inclusive and end exclusive so it can be used to
+ * determine compressed size of a given extent by its start and start of the
+ * next extent easily, without counting length.
+ * Whole file is specified as start = 0, end = (u64)-1
+ */
+static long btrfs_ioctl_compr_size(struct file *file, void __user *argp)
+{
+	struct inode *inode = fdentry(file)->d_inode;
+	struct btrfs_ioctl_compr_size_args compr_args;
+	u64 len;
+	u64 compressed_size = 0;
+	u64 offset = 0;
+
+	if (S_ISDIR(inode->i_mode))
+		return -EISDIR;
+
+	if (copy_from_user(&compr_args, argp,
+				sizeof(struct btrfs_ioctl_compr_size_args)))
+		return -EFAULT;
+
+	if (compr_args.start > compr_args.end)
+		return -EINVAL;
+
+	mutex_lock(&inode->i_mutex);
+
+	offset = compr_args.start;
+	if (inode->i_size > compr_args.end)
+		len = compr_args.end;
+	else
+		len = inode->i_size;
+
+	/*
+	 * do any pending delalloc/csum calc on inode, one way or
+	 * another, and lock file content
+	 */
+	btrfs_wait_ordered_range(inode, compr_args.start, len);
+
+	while (offset < len) {
+		struct extent_map *em;
+
+		em = btrfs_get_extent(inode, NULL, 0, offset, 1, 0);
+		if (IS_ERR_OR_NULL(em))
+			goto error;
+		if (em->block_len != (u64)-1)
+			compressed_size += em->block_len;
+		else if (em->block_start == EXTENT_MAP_INLINE) {
+			compressed_size += ALIGN(em->len, 512);
+		}
+		offset += em->len;
+		free_extent_map(em);
+	}
+	mutex_unlock(&inode->i_mutex);
+
+	unlock_extent(&BTRFS_I(inode)->io_tree, compr_args.start, len, GFP_NOFS);
+
+	compr_args.size = compressed_size >> 9;
+
+	if (copy_to_user(argp, &compr_args, sizeof(struct
+					btrfs_ioctl_compr_size_args)))
+		return -EFAULT;
+
+	return 0;
+
+error:
+	mutex_unlock(&inode->i_mutex);
+	unlock_extent(&BTRFS_I(inode)->io_tree, compr_args.start, len, GFP_NOFS);
+
+	return -EIO;
+}
+
 static long btrfs_ioctl_logical_to_ino(struct btrfs_root *root,
 					void __user *arg)
 {
@@ -3110,6 +3185,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_scrub_cancel(root, argp);
 	case BTRFS_IOC_SCRUB_PROGRESS:
 		return btrfs_ioctl_scrub_progress(root, argp);
+	case BTRFS_IOC_COMPR_SIZE:
+		return btrfs_ioctl_compr_size(file, argp);
 	}
 
 	return -ENOTTY;
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index 252ae99..bce761c 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -217,6 +217,15 @@ struct btrfs_ioctl_logical_ino_args {
 	__u64				inodes;
 };
 
+struct btrfs_ioctl_compr_size_args {
+	/* Range start, inclusive */
+	__u64				start;		/* in */
+	/* Range end, exclusive */
+	__u64				end;		/* in */
+	__u64				size;		/* out */
+	__u64				reserved[2];
+};
+
 #define BTRFS_IOC_SNAP_CREATE _IOW(BTRFS_IOCTL_MAGIC, 1, \
 				   struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_DEFRAG _IOW(BTRFS_IOCTL_MAGIC, 2, \
@@ -276,5 +285,7 @@ struct btrfs_ioctl_logical_ino_args {
 					struct btrfs_ioctl_ino_path_args)
 #define BTRFS_IOC_LOGICAL_INO _IOWR(BTRFS_IOCTL_MAGIC, 36, \
 					struct btrfs_ioctl_ino_path_args)
+#define BTRFS_IOC_COMPR_SIZE _IOR(BTRFS_IOCTL_MAGIC, 51, \
+				struct btrfs_ioctl_compr_size_args)
 
 #endif
-- 
1.7.7.3