Merge patch series "iomap: allow the file system to submit the writeback bios"

Christoph Hellwig <hch@lst.de> says:

This series contains the iomap prep work to support zoned XFS.

The biggest changes are:

 - an option to reuse the ioend code for direct writes in addition to the
   current use for buffered writeback, which allows the file system to
   track completions on a per-bio basis instead of the current end_io
   callback which operates on the entire I/O.
   Note that it might make sense to split the ioend code from
   buffered-io.c into its own file with this.  Let me know what you think
   of that and I can include it in the next version
 - change of the writeback_ops so that the submit_bio call can be done by
   the file system.  Note that btrfs will also need this eventually when
   it starts using iomap
 - helpers to split ioend to the zone append queue_limits that plug
   into the previous item above.
 - a new ANON_WRITE flags for writes that don't have a block number
   assigned to them at the iomap level, leaving the file system to do
   that work in the submission handler.  Note that btrfs wants something
   similar also for compressed I/O, which should be able to reuse this,
   maybe with minor tweaks.
 - passing private data to a few more helper

The XFS changes to use this will be posted to the xfs list only to not
spam fsdevel too much.

* patches from https://lore.kernel.org/r/20250206064035.2323428-2-hch@lst.de:
  iomap: pass private data to iomap_truncate_page
  iomap: pass private data to iomap_zero_range
  iomap: pass private data to iomap_page_mkwrite
  iomap: add a io_private field to struct iomap_ioend
  iomap: optionally use ioends for direct I/O
  iomap: factor out a iomap_dio_done helper
  iomap: move common ioend code to ioend.c
  iomap: split bios to zone append limits in the submission handlers
  iomap: add a IOMAP_F_ANON_WRITE flag
  iomap: simplify io_flags and io_type in struct iomap_ioend
  iomap: allow the file system to submit the writeback bios

Link: https://lore.kernel.org/r/20250206064035.2323428-2-hch@lst.de
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

Documentation/filesystems/iomap/design.rst

@@ -246,6 +246,10 @@ The fields are as follows:
    * **IOMAP_F_PRIVATE**: Starting with this value, the upper bits can
      be set by the filesystem for its own purposes.
 
+   * **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.
+
    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:

Documentation/filesystems/iomap/operations.rst

@@ -283,7 +283,7 @@ The ``ops`` structure must be specified and is as follows:
  struct iomap_writeback_ops {
      int (*map_blocks)(struct iomap_writepage_ctx *wpc, struct inode *inode,
                        loff_t offset, unsigned len);
-     int (*prepare_ioend)(struct iomap_ioend *ioend, int status);
+     int (*submit_ioend)(struct iomap_writepage_ctx *wpc, int status);
      void (*discard_folio)(struct folio *folio, loff_t pos);
  };
 
@@ -306,13 +306,12 @@ The fields are as follows:
     purpose.
     This function must be supplied by the filesystem.
 
-  - ``prepare_ioend``: Enables filesystems to transform the writeback
-    ioend or perform any other preparatory work before the writeback I/O
-    is submitted.
+  - ``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.
+    transactions from process context before submitting the bio.
     This function is optional.
 
   - ``discard_folio``: iomap calls this function after ``->map_blocks``
@@ -341,7 +340,7 @@ 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 ``->prepare_ioend`` function to
+extent conversions) should provide a ``->submit_ioend`` function to
 set ``struct iomap_end::bio::bi_end_io`` to its own function.
 This function should call ``iomap_finish_ioends`` after finishing its
 own work (e.g. unwritten extent conversion).

fs/gfs2/bmap.c

@@ -1300,7 +1300,8 @@ static int gfs2_block_zero_range(struct inode *inode, loff_t from,
 				 unsigned int length)
 {
 	BUG_ON(current->journal_info);
-	return iomap_zero_range(inode, from, length, NULL, &gfs2_iomap_ops);
+	return iomap_zero_range(inode, from, length, NULL, &gfs2_iomap_ops,
+			NULL);
 }
 
 #define GFS2_JTRUNC_REVOKES 8192

fs/iomap/Makefile

@@ -12,6 +12,7 @@ iomap-y				+= trace.o \
 				   iter.o
 iomap-$(CONFIG_BLOCK)		+= buffered-io.o \
 				   direct-io.o \
+				   ioend.o \
 				   fiemap.o \
 				   seek.o
 iomap-$(CONFIG_SWAP)		+= swapfile.o