btrfs: nowait aio support

Return EAGAIN if any of the following checks fail
 + i_rwsem is not lockable
 + NODATACOW or PREALLOC is not set
 + Cannot nocow at the desired location
 + Writing beyond end of file which is not allocated

Acked-by: David Sterba <dsterba@suse.com>
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 30 insertions, 6 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index da1096eb1a40..59e2dccdf75b 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1875,12 +1875,29 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
         ssize_t num_written = 0;
         bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
         ssize_t err;
-        loff_t pos;
-        size_t count;
+        loff_t pos = iocb->ki_pos;
+        size_t count = iov_iter_count(from);
         loff_t oldsize;
         int clean_page = 0;
 
-        inode_lock(inode);
+        if ((iocb->ki_flags & IOCB_NOWAIT) &&
+                        (iocb->ki_flags & IOCB_DIRECT)) {
+                /* Don't sleep on inode rwsem */
+                if (!inode_trylock(inode))
+                        return -EAGAIN;
+                /*
+                 * We will allocate space in case nodatacow is not set,
+                 * so bail
+                 */
+                if (!(BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW |
+                                              BTRFS_INODE_PREALLOC)) ||
+                    check_can_nocow(BTRFS_I(inode), pos, &count) <= 0) {
+                        inode_unlock(inode);
+                        return -EAGAIN;
+                }
+        } else
+                inode_lock(inode);
+
         err = generic_write_checks(iocb, from);
         if (err <= 0) {
                 inode_unlock(inode);
@@ -1914,8 +1931,6 @@ 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, fs_info->sectorsize);
         oldsize = i_size_read(inode);
         if (start_pos > oldsize) {
@@ -3071,13 +3086,19 @@ out:
         return offset;
 }
 
+static int btrfs_file_open(struct inode *inode, struct file *filp)
+{
+        filp->f_mode |= FMODE_AIO_NOWAIT;
+        return generic_file_open(inode, filp);
+}
+
 const struct file_operations btrfs_file_operations = {
         .llseek         = btrfs_file_llseek,
         .read_iter      = generic_file_read_iter,
         .splice_read    = generic_file_splice_read,
         .write_iter     = btrfs_file_write_iter,
         .mmap           = btrfs_file_mmap,
-        .open           = generic_file_open,
+        .open           = btrfs_file_open,
         .release        = btrfs_release_file,
         .fsync          = btrfs_sync_file,
         .fallocate      = btrfs_fallocate,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f942293dd7e7..556c93060606 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8754,6 +8754,9 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
                         dio_data.overwrite = 1;
                         inode_unlock(inode);
                         relock = true;
+                } else if (iocb->ki_flags & IOCB_NOWAIT) {
+                        ret = -EAGAIN;
+                        goto out;
                 }
                 ret = btrfs_delalloc_reserve_space(inode, offset, count);
                 if (ret)