On 03/04/2025 19:22, Ritesh Harjani (IBM) wrote:
IMHO, This document seems to be updated a lot, to the point where I
think that it has too much detail.
Let's document the use of these flags in iomap design doc where other
flags are defined too -
- IOMAP_F_BOUNDARY was added by XFS to prevent merging of ioends
across RTG boundaries.
- IOMAP_F_ATOMIC_BIO was added for supporting atomic I/O operations
for filesystems to inform the iomap that it needs HW-offload based
mechanism for torn-write protection
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
---
Documentation/filesystems/iomap/design.rst | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/Documentation/filesystems/iomap/design.rst b/Documentation/filesystems/iomap/design.rst
index e29651a42eec..b916e85bc930 100644
--- a/Documentation/filesystems/iomap/design.rst
+++ b/Documentation/filesystems/iomap/design.rst
@@ -243,6 +243,11 @@ The fields are as follows:
regular file data.
This is only useful for FIEMAP.
+ * **IOMAP_F_BOUNDARY**: This indicates that I/O and I/O completions
+ for this iomap must never be merged with the mapping before it.
This is just effectively the same comment as in the code - what's the
use in this?
+ Currently XFS uses this to prevent merging of ioends across RTG
+ (realtime group) boundaries.
+
* **IOMAP_F_PRIVATE**: Starting with this value, the upper bits can
be set by the filesystem for its own purposes.
Is this comment now out of date according to your change in 923936efeb74?
@@ -250,6 +255,11 @@ The fields are as follows:
block assigned to it yet and the file system will do that in the bio
submission handler, splitting the I/O as needed.
+ * **IOMAP_F_ATOMIC_BIO**: Indicates that write I/O must be submitted
+ with the ``REQ_ATOMIC`` flag set in the bio.
This is effectively the same comment as iomap.h
Filesystems need to set
+ this flag to inform iomap that the write I/O operation requires
+ torn-write protection based on HW-offload mechanism.
Personally I think that this is obvious. If not, the reader should check
the xfs and ext4 example in the code.
+
These flags can be set by iomap itself during file operations.
The filesystem should supply an ``->iomap_end`` function if it needs
to observe these flags:
