On Wed, Sep 11, 2019 at 01:38:52PM +0530, Ritesh Harjani wrote:

On 9/9/19 2:56 PM, Ritesh Harjani wrote:

quoted

On 9/9/19 4:49 AM, Matthew Bobrowski wrote:

quoted

@@ -217,6 +218,14 @@ static ssize_t ext4_write_checks(struct kiocb

*iocb, struct iov_iter *from)
      if (ret <= 0)
          return ret;

+    ret = file_remove_privs(iocb->ki_filp);
+    if (ret)
+        return 0;
+
+    ret = file_update_time(iocb->ki_filp);
+    if (ret)
+        return 0;
+
      if (unlikely(IS_IMMUTABLE(inode)))
          return -EPERM;

Maybe we can move this up. If file is IMMUTABLE no point in
calling for above actions (file_remove_privs/file_updatetime).

Yep, sure could do this. In fact, I think we could put this above
generic_write_checks().

Also why not use file_modified() API which does the same.

Ah, nice. Indeed we can, thanks for simplifying it.

quoted

quoted

@@ -234,6 +243,34 @@ static ssize_t ext4_write_checks(struct kiocb

*iocb, struct iov_iter *from)
      return iov_iter_count(from);
  }

+static ssize_t ext4_buffered_write_iter(struct kiocb *iocb,
+                    struct iov_iter *from)
+{
+    ssize_t ret;
+    struct inode *inode = file_inode(iocb->ki_filp);
+
+    if (iocb->ki_flags & IOCB_NOWAIT)
+        return -EOPNOTSUPP;
+
+    if (!inode_trylock(inode))
+        inode_lock(inode);

Is it really needed to check for trylock first?
we can directly call for inode_lock() here.

You're right, no need to do this dance. We can call inode_lock() directly.

quoted

quoted

+
+    ret = ext4_write_checks(iocb, from);
+    if (ret <= 0)
+        goto out;
+
+    current->backing_dev_info = inode_to_bdi(inode);
+    ret = generic_perform_write(iocb->ki_filp, from, iocb->ki_pos);
+    current->backing_dev_info = NULL;
+out:
+    inode_unlock(inode);
+    if (likely(ret > 0)) {
+        iocb->ki_pos += ret;
+        ret = generic_write_sync(iocb, ret);
+    }
+    return ret;
+}
+
+    if (!ext4_dio_checks(inode)) {
+        inode_unlock(inode);
+        /*
+         * Fallback to buffered IO if the operation on the
+         * inode is not supported by direct IO.
+         */
+        return ext4_buffered_write_iter(iocb, from);
+    }
+
+    ret = ext4_write_checks(iocb, from);

This can modify the count in iov_iter *from.

Good point. We'll recalculate the iter 'count' again.

Thank you for the review/suggestions, highly appreciated.

--<M>--