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Diffstat (limited to 'Documentation/filesystems/iomap/operations.rst')
| -rw-r--r-- | Documentation/filesystems/iomap/operations.rst | 57 |
1 files changed, 28 insertions, 29 deletions
diff --git a/Documentation/filesystems/iomap/operations.rst b/Documentation/filesystems/iomap/operations.rst index 3b628e370d88..067ed8e14ef3 100644 --- a/Documentation/filesystems/iomap/operations.rst +++ b/Documentation/filesystems/iomap/operations.rst @@ -57,21 +57,19 @@ The following address space operations can be wrapped easily: * ``bmap`` * ``swap_activate`` -``struct iomap_folio_ops`` +``struct iomap_write_ops`` -------------------------- -The ``->iomap_begin`` function for pagecache operations may set the -``struct iomap::folio_ops`` field to an ops structure to override -default behaviors of iomap: - .. code-block:: c - struct iomap_folio_ops { + struct iomap_write_ops { struct folio *(*get_folio)(struct iomap_iter *iter, loff_t pos, unsigned len); void (*put_folio)(struct inode *inode, loff_t pos, unsigned copied, struct folio *folio); bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap); + int (*read_folio_range)(const struct iomap_iter *iter, + struct folio *folio, loff_t pos, size_t len); }; iomap calls these functions: @@ -127,6 +125,10 @@ iomap calls these functions: ``->iomap_valid``, then the iomap should considered stale and the validation failed. + - ``read_folio_range``: Called to synchronously read in the range that will + be written to. If this function is not provided, iomap will default to + submitting a bio read request. + These ``struct kiocb`` flags are significant for buffered I/O with iomap: * ``IOCB_NOWAIT``: Turns on ``IOMAP_NOWAIT``. @@ -271,7 +273,7 @@ writeback. It does not lock ``i_rwsem`` or ``invalidate_lock``. The dirty bit will be cleared for all folios run through the -``->map_blocks`` machinery described below even if the writeback fails. +``->writeback_range`` machinery described below even if the writeback fails. This is to prevent dirty folio clots when storage devices fail; an ``-EIO`` is recorded for userspace to collect via ``fsync``. @@ -283,15 +285,14 @@ The ``ops`` structure must be specified and is as follows: .. code-block:: c struct iomap_writeback_ops { - int (*map_blocks)(struct iomap_writepage_ctx *wpc, struct inode *inode, - loff_t offset, unsigned len); - int (*submit_ioend)(struct iomap_writepage_ctx *wpc, int status); - void (*discard_folio)(struct folio *folio, loff_t pos); + int (*writeback_range)(struct iomap_writepage_ctx *wpc, + struct folio *folio, u64 pos, unsigned int len, u64 end_pos); + int (*writeback_submit)(struct iomap_writepage_ctx *wpc, int error); }; The fields are as follows: - - ``map_blocks``: Sets ``wpc->iomap`` to the space mapping of the file + - ``writeback_range``: Sets ``wpc->iomap`` to the space mapping of the file range (in bytes) given by ``offset`` and ``len``. iomap calls this function for each dirty fs block in each dirty folio, though it will `reuse mappings @@ -306,27 +307,26 @@ The fields are as follows: This revalidation must be open-coded by the filesystem; it is unclear if ``iomap::validity_cookie`` can be reused for this purpose. - This function must be supplied by the filesystem. - - - ``submit_ioend``: Allows the file systems to hook into writeback bio - submission. - This might include pre-write space accounting updates, or installing - a custom ``->bi_end_io`` function for internal purposes, such as - deferring the ioend completion to a workqueue to run metadata update - transactions from process context before submitting the bio. - This function is optional. - - ``discard_folio``: iomap calls this function after ``->map_blocks`` - fails to schedule I/O for any part of a dirty folio. - The function should throw away any reservations that may have been - made for the write. + If this methods fails to schedule I/O for any part of a dirty folio, it + should throw away any reservations that may have been made for the write. The folio will be marked clean and an ``-EIO`` recorded in the pagecache. Filesystems can use this callback to `remove <https://lore.kernel.org/all/20201029163313.1766967-1-bfoster@redhat.com/>`_ delalloc reservations to avoid having delalloc reservations for clean pagecache. - This function is optional. + This function must be supplied by the filesystem. + + - ``writeback_submit``: Submit the previous built writeback context. + Block based file systems should use the iomap_ioend_writeback_submit + helper, other file system can implement their own. + File systems can optionall to hook into writeback bio submission. + This might include pre-write space accounting updates, or installing + a custom ``->bi_end_io`` function for internal purposes, such as + deferring the ioend completion to a workqueue to run metadata update + transactions from process context before submitting the bio. + This function must be supplied by the filesystem. Pagecache Writeback Completion ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -340,10 +340,9 @@ If the write failed, it will also set the error bits on the folios and the address space. This can happen in interrupt or process context, depending on the storage device. - Filesystems that need to update internal bookkeeping (e.g. unwritten -extent conversions) should provide a ``->submit_ioend`` function to -set ``struct iomap_end::bio::bi_end_io`` to its own function. +extent conversions) should set their own bi_end_io on the bios +submitted by ``->submit_writeback`` This function should call ``iomap_finish_ioends`` after finishing its own work (e.g. unwritten extent conversion). |