On Thu, Apr 03, 2025 at 11:52:27PM +0530, Ritesh Harjani (IBM) wrote: > 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. > + Currently XFS uses this to prevent merging of ioends across RTG > + (realtime group) boundaries. Hrm, ok. Based on hch's comment about not mentioning specific fs behavior, I think I'll suggest something more like: IOMAP_F_BOUNDARY: This 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**: Starting with this value, the upper bits can > be set by the filesystem for its own purposes. > > @@ -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. 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. --D > + > 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 > >
