switch generic_write_checks() to iocb and iter

... returning -E... upon error and amount of data left in iter after
(possible) truncation upon success.  Note, that normal case gives
a non-zero (positive) return value, so any tests for != 0 _must_ be
updated.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Conflicts:
	fs/ext4/file.c

1 files changed, 9 insertions, 15 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 691a84a81e09..c64d11c41eeb 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1739,27 +1739,19 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
         u64 start_pos;
         u64 end_pos;
         ssize_t num_written = 0;
-        ssize_t err = 0;
-        size_t count = iov_iter_count(from);
         bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
-        loff_t pos = iocb->ki_pos;
+        ssize_t err;
+        loff_t pos;
+        size_t count;
 
         mutex_lock(&inode->i_mutex);
-
-        current->backing_dev_info = inode_to_bdi(inode);
-        err = generic_write_checks(file, &pos, &count);
-        if (err) {
+        err = generic_write_checks(iocb, from);
+        if (err <= 0) {
                 mutex_unlock(&inode->i_mutex);
-                goto out;
-        }
-
-        if (count == 0) {
-                mutex_unlock(&inode->i_mutex);
-                goto out;
+                return err;
         }
 
-        iov_iter_truncate(from, count);
-
+        current->backing_dev_info = inode_to_bdi(inode);
         err = file_remove_suid(file);
         if (err) {
                 mutex_unlock(&inode->i_mutex);
@@ -1786,6 +1778,8 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
          */
         update_time_for_write(inode);
 
+        pos = iocb->ki_pos;
+        count = iov_iter_count(from);
         start_pos = round_down(pos, root->sectorsize);
         if (start_pos > i_size_read(inode)) {
                 /* Expand hole size to cover write data, preventing empty gap */