fs: Add new flag(FALLOC_FL_COLLAPSE_RANGE) for fallocate

This patch is in response of the following post:
http://lwn.net/Articles/556136/
"ext4: introduce two new ioctls"

Dave chinner suggested that truncate_block_range
(which was one of the ioctls name) should be a fallocate operation
and not any fs specific ioctl, hence we add this functionality to new flags of fallocate.

This new functionality of collapsing range could be used by media editing tools
which does non linear editing to quickly purge and edit parts of a media file.
This will immensely improve the performance of these operations.
The limitation of fs block size aligned offsets can be easily handled
by media codecs which are encapsulated in a conatiner as they have to
just change the offset to next keyframe value to match the proper alignment.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 21 insertions, 3 deletions

diff --git a/fs/open.c b/fs/open.c
index 4b3e1edf2fe4..4a923a547d10 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -231,7 +231,8 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
                 return -EINVAL;
 
         /* Return error if mode is not supported */
-        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
+        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
+                     FALLOC_FL_COLLAPSE_RANGE))
                 return -EOPNOTSUPP;
 
         /* Punch hole must have keep size set */
@@ -239,11 +240,20 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
             !(mode & FALLOC_FL_KEEP_SIZE))
                 return -EOPNOTSUPP;
 
+        /* Collapse range should only be used exclusively. */
+        if ((mode & FALLOC_FL_COLLAPSE_RANGE) &&
+            (mode & ~FALLOC_FL_COLLAPSE_RANGE))
+                return -EINVAL;
+
         if (!(file->f_mode & FMODE_WRITE))
                 return -EBADF;
 
-        /* It's not possible punch hole on append only file */
-        if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
+        /*
+         * It's not possible to punch hole or perform collapse range
+         * on append only file
+         */
+        if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_COLLAPSE_RANGE)
+            && IS_APPEND(inode))
                 return -EPERM;
 
         if (IS_IMMUTABLE(inode))
@@ -271,6 +281,14 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
         if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
                 return -EFBIG;
 
+        /*
+         * There is no need to overlap collapse range with EOF, in which case
+         * it is effectively a truncate operation
+         */
+        if ((mode & FALLOC_FL_COLLAPSE_RANGE) &&
+            (offset + len >= i_size_read(inode)))
+                return -EINVAL;
+
         if (!file->f_op->fallocate)
                 return -EOPNOTSUPP;