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 I/O and I/O
completions 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.
While we are at it, let's also fix the description of IOMAP_F_PRIVATE
flag after a recent:
commit 923936efeb74b3 ("iomap: Fix conflicting values of iomap flags")
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
---
Documentation/filesystems/iomap/design.rst | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/Documentation/filesystems/iomap/design.rst b/Documentation/filesystems/iomap/design.rst
index e29651a42eec..f2df9b6df988 100644
--- a/Documentation/filesystems/iomap/design.rst
+++ b/Documentation/filesystems/iomap/design.rst
@@ -243,13 +243,25 @@ The fields are as follows:
regular file data.
This is only useful for FIEMAP.
- * **IOMAP_F_PRIVATE**: Starting with this value, the upper bits can
- be set by the filesystem for its own purposes.
+ * **IOMAP_F_BOUNDARY**: This indicates I/O and its completion must not be
+ merged with any other I/O or completion. Filesystems must use this when
+ submitting I/O to devices that cannot handle I/O crossing certain LBAs
+ (e.g. ZNS devices). This flag applies only to buffered I/O writeback; all
+ other functions ignore it.
+
+ * **IOMAP_F_PRIVATE**: This flag is reserved for filesystem private use.
* **IOMAP_F_ANON_WRITE**: Indicates that (write) I/O does not have a target
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**: This indicates write I/O must be submitted with the
+ ``REQ_ATOMIC`` flag set in the bio. Filesystems need to set this flag to
+ inform iomap that the write I/O operation requires torn-write protection
+ based on HW-offload mechanism. They must also ensure that mapping updates
+ upon the completion of the I/O must be performed in a single metadata
+ update.
+
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:
--
2.48.1
