Re: [PATCH v4 01/22] fs: Add generic_atomic_write_valid_size()

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On 12/06/2024 22:10, Darrick J. Wong wrote:
On Fri, Jun 07, 2024 at 02:38:58PM +0000, John Garry wrote:
Add a generic helper for FSes to validate that an atomic write is
appropriately sized (along with the other checks).

Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
  include/linux/fs.h | 12 ++++++++++++
  1 file changed, 12 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 069cbab62700..e13d34f8c24e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3645,4 +3645,16 @@ bool generic_atomic_write_valid(loff_t pos, struct iov_iter *iter)
  	return true;
  }
+static inline
+bool generic_atomic_write_valid_size(loff_t pos, struct iov_iter *iter,
+				unsigned int unit_min, unsigned int unit_max)
+{
+	size_t len = iov_iter_count(iter);
+
+	if (len < unit_min || len > unit_max)
+		return false;
+
+	return generic_atomic_write_valid(pos, iter);
+}

Now that I look back at "fs: Initial atomic write support" I wonder why
not pass the iocb and the iov_iter instead of pos and the iov_iter?

The original user of generic_atomic_write_valid() [blkdev_dio_unaligned() or blkdev_dio_invalid() with the rename] used these same args, so I just went with that.

And can these be collapsed into a single generic_atomic_write_checks()
function?

bdev file operations would then need to use generic_atomic_write_valid_size(), and there is no unit_min and unit_max size there, apart from bdev awu min and max. And if I checked them, we would be duplicating checks (of awu min and max) in the block layer.

Cheers,
John




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