ext4: nowait aio support

Return EAGAIN if any of the following checks fail for direct I/O:
  + i_rwsem is lockable
  + Writing beyond end of file (will trigger allocation)
  + Blocks are not allocated at the write location

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 29 insertions, 6 deletions

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 02ce7e7bbdf5..58e2eeaa0bc4 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -37,7 +37,11 @@ static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
         struct inode *inode = file_inode(iocb->ki_filp);
         ssize_t ret;
 
-        inode_lock_shared(inode);
+        if (!inode_trylock_shared(inode)) {
+                if (iocb->ki_flags & IOCB_NOWAIT)
+                        return -EAGAIN;
+                inode_lock_shared(inode);
+        }
         /*
          * Recheck under inode lock - at this point we are sure it cannot
          * change anymore
@@ -179,7 +183,11 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
         struct inode *inode = file_inode(iocb->ki_filp);
         ssize_t ret;
 
-        inode_lock(inode);
+        if (!inode_trylock(inode)) {
+                if (iocb->ki_flags & IOCB_NOWAIT)
+                        return -EAGAIN;
+                inode_lock(inode);
+        }
         ret = ext4_write_checks(iocb, from);
         if (ret <= 0)
                 goto out;
@@ -216,7 +224,12 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
                 return ext4_dax_write_iter(iocb, from);
 #endif
 
-        inode_lock(inode);
+        if (!inode_trylock(inode)) {
+                if (iocb->ki_flags & IOCB_NOWAIT)
+                        return -EAGAIN;
+                inode_lock(inode);
+        }
+
         ret = ext4_write_checks(iocb, from);
         if (ret <= 0)
                 goto out;
@@ -235,9 +248,15 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 
         iocb->private = &overwrite;
         /* Check whether we do a DIO overwrite or not */
-        if (o_direct && ext4_should_dioread_nolock(inode) && !unaligned_aio &&
-            ext4_overwrite_io(inode, iocb->ki_pos, iov_iter_count(from)))
-                overwrite = 1;
+        if (o_direct && !unaligned_aio) {
+                if (ext4_overwrite_io(inode, iocb->ki_pos, iov_iter_count(from))) {
+                        if (ext4_should_dioread_nolock(inode))
+                                overwrite = 1;
+                } else if (iocb->ki_flags & IOCB_NOWAIT) {
+                        ret = -EAGAIN;
+                        goto out;
+                }
+        }
 
         ret = __generic_file_write_iter(iocb, from);
         inode_unlock(inode);
@@ -435,6 +454,10 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
                 if (ret < 0)
                         return ret;
         }
+
+        /* Set the flags to support nowait AIO */
+        filp->f_mode |= FMODE_AIO_NOWAIT;
+
         return dquot_file_open(inode, filp);
 }