Merge tag 'vfs-6.11.iomap' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull iomap updates from Christian Brauner:
 "This contains some minor work for the iomap subsystem:

   - Add documentation on the design of iomap and how to port to it

   - Optimize iomap_read_folio()

   - Bring back the change to iomap_write_end() to no increase i_size.

     This is accompanied by a change to xfs to reserve blocks for
     truncating large realtime inodes to avoid exposing stale data when
     iomap_write_end() stops increasing i_size"

* tag 'vfs-6.11.iomap' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  iomap: don't increase i_size in iomap_write_end()
  xfs: reserve blocks for truncating large realtime inode
  Documentation: the design of iomap and how to port
  iomap: Optimize iomap_read_folio

Documentation/filesystems/index.rst

@@ -34,6 +34,7 @@ algorithms work.
    seq_file
    sharedsubtree
    idmappings
+   iomap/index
 
    automount-support
 

Documentation/filesystems/iomap/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+=======================
+VFS iomap Documentation
+=======================
+
+.. toctree::
+   :maxdepth: 2
+   :numbered:
+
+   design
+   operations
+   porting

Documentation/filesystems/iomap/porting.rst

+.. SPDX-License-Identifier: GPL-2.0
+.. _iomap_porting:
+
+..
+        Dumb style notes to maintain the author's sanity:
+        Please try to start sentences on separate lines so that
+        sentence changes don't bleed colors in diff.
+        Heading decorations are documented in sphinx.rst.
+
+=======================
+Porting Your Filesystem
+=======================
+
+.. contents:: Table of Contents
+   :local:
+
+Why Convert?
+============
+
+There are several reasons to convert a filesystem to iomap:
+
+ 1. The classic Linux I/O path is not terribly efficient.
+    Pagecache operations lock a single base page at a time and then call
+    into the filesystem to return a mapping for only that page.
+    Direct I/O operations build I/O requests a single file block at a
+    time.
+    This worked well enough for direct/indirect-mapped filesystems such
+    as ext2, but is very inefficient for extent-based filesystems such
+    as XFS.
+
+ 2. Large folios are only supported via iomap; there are no plans to
+    convert the old buffer_head path to use them.
+
+ 3. Direct access to storage on memory-like devices (fsdax) is only
+    supported via iomap.
+
+ 4. Lower maintenance overhead for individual filesystem maintainers.
+    iomap handles common pagecache related operations itself, such as
+    allocating, instantiating, locking, and unlocking of folios.
+    No ->write_begin(), ->write_end() or direct_IO
+    address_space_operations are required to be implemented by
+    filesystem using iomap.
+
+How Do I Convert a Filesystem?
+==============================
+
+First, add ``#include <linux/iomap.h>`` from your source code and add
+``select FS_IOMAP`` to your filesystem's Kconfig option.
+Build the kernel, run fstests with the ``-g all`` option across a wide
+variety of your filesystem's supported configurations to build a
+baseline of which tests pass and which ones fail.
+
+The recommended approach is first to implement ``->iomap_begin`` (and
+``->iomap_end`` if necessary) to allow iomap to obtain a read-only
+mapping of a file range.
+In most cases, this is a relatively trivial conversion of the existing
+``get_block()`` function for read-only mappings.
+``FS_IOC_FIEMAP`` is a good first target because it is trivial to
+implement support for it and then to determine that the extent map
+iteration is correct from userspace.
+If FIEMAP is returning the correct information, it's a good sign that
+other read-only mapping operations will do the right thing.
+
+Next, modify the filesystem's ``get_block(create = false)``
+implementation to use the new ``->iomap_begin`` implementation to map
+file space for selected read operations.
+Hide behind a debugging knob the ability to switch on the iomap mapping
+functions for selected call paths.
+It is necessary to write some code to fill out the bufferhead-based
+mapping information from the ``iomap`` structure, but the new functions
+can be tested without needing to implement any iomap APIs.
+
+Once the read-only functions are working like this, convert each high
+level file operation one by one to use iomap native APIs instead of
+going through ``get_block()``.
+Done one at a time, regressions should be self evident.
+You *do* have a regression test baseline for fstests, right?
+It is suggested to convert swap file activation, ``SEEK_DATA``, and
+``SEEK_HOLE`` before tackling the I/O paths.
+A likely complexity at this point will be converting the buffered read
+I/O path because of bufferheads.
+The buffered read I/O paths doesn't need to be converted yet, though the
+direct I/O read path should be converted in this phase.
+
+At this point, you should look over your ``->iomap_begin`` function.
+If it switches between large blocks of code based on dispatching of the
+``flags`` argument, you should consider breaking it up into
+per-operation iomap ops with smaller, more cohesive functions.
+XFS is a good example of this.
+
+The next thing to do is implement ``get_blocks(create == true)``
+functionality in the ``->iomap_begin``/``->iomap_end`` methods.
+It is strongly recommended to create separate mapping functions and
+iomap ops for write operations.
+Then convert the direct I/O write path to iomap, and start running fsx
+w/ DIO enabled in earnest on filesystem.
+This will flush out lots of data integrity corner case bugs that the new
+write mapping implementation introduces.
+
+Now, convert any remaining file operations to call the iomap functions.
+This will get the entire filesystem using the new mapping functions, and
+they should largely be debugged and working correctly after this step.
+
+Most likely at this point, the buffered read and write paths will still
+need to be converted.
+The mapping functions should all work correctly, so all that needs to be
+done is rewriting all the code that interfaces with bufferheads to
+interface with iomap and folios.
+It is much easier first to get regular file I/O (without any fancy
+features like fscrypt, fsverity, compression, or data=journaling)
+converted to use iomap.
+Some of those fancy features (fscrypt and compression) aren't
+implemented yet in iomap.
+For unjournalled filesystems that use the pagecache for symbolic links
+and directories, you might also try converting their handling to iomap.
+
+The rest is left as an exercise for the reader, as it will be different
+for every filesystem.
+If you encounter problems, email the people and lists in
+``get_maintainers.pl`` for help.

MAINTAINERS

@@ -8460,6 +8460,7 @@ R:	Darrick J. Wong <djwong@kernel.org>
 L:	linux-xfs@vger.kernel.org
 L:	linux-fsdevel@vger.kernel.org
 S:	Supported
+F:	Documentation/filesystems/iomap/*
 F:	fs/iomap/
 F:	include/linux/iomap.h
 

fs/iomap/buffered-io.c

@@ -442,6 +442,24 @@ static loff_t iomap_readpage_iter(const struct iomap_iter *iter,
 	return pos - orig_pos + plen;
 }
 
+static loff_t iomap_read_folio_iter(const struct iomap_iter *iter,
+		struct iomap_readpage_ctx *ctx)
+{
+	struct folio *folio = ctx->cur_folio;
+	size_t offset = offset_in_folio(folio, iter->pos);
+	loff_t length = min_t(loff_t, folio_size(folio) - offset,
+			      iomap_length(iter));
+	loff_t done, ret;
+
+	for (done = 0; done < length; done += ret) {
+		ret = iomap_readpage_iter(iter, ctx, done);
+		if (ret <= 0)
+			return ret;
+	}
+
+	return done;
+}
+
 int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 {
 	struct iomap_iter iter = {
@@ -457,7 +475,7 @@ int iomap_read_folio(struct folio *folio, const struct iomap_ops *ops)
 	trace_iomap_readpage(iter.inode, 1);
 
 	while ((ret = iomap_iter(&iter, ops)) > 0)
-		iter.processed = iomap_readpage_iter(&iter, &ctx, 0);
+		iter.processed = iomap_read_folio_iter(&iter, &ctx);
 
 	if (ctx.bio) {
 		submit_bio(ctx.bio);
@@ -872,37 +890,22 @@ static bool iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
 		size_t copied, struct folio *folio)
 {
 	const struct iomap *srcmap = iomap_iter_srcmap(iter);
-	loff_t old_size = iter->inode->i_size;
-	size_t written;
 
 	if (srcmap->type == IOMAP_INLINE) {
 		iomap_write_end_inline(iter, folio, pos, copied);
-		written = copied;
-	} else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
-		written = block_write_end(NULL, iter->inode->i_mapping, pos,
-					len, copied, &folio->page, NULL);
-		WARN_ON_ONCE(written != copied && written != 0);
-	} else {
-		written = __iomap_write_end(iter->inode, pos, len, copied,
-					    folio) ? copied : 0;
+		return true;
 	}
 
-	/*
-	 * Update the in-memory inode size after copying the data into the page
-	 * cache.  It's up to the file system to write the updated size to disk,
-	 * preferably after I/O completion so that no stale data is exposed.
-	 * Only once that's done can we unlock and release the folio.
-	 */
-	if (pos + written > old_size) {
-		i_size_write(iter->inode, pos + written);
-		iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
-	}
-	__iomap_put_folio(iter, pos, written, folio);
+	if (srcmap->flags & IOMAP_F_BUFFER_HEAD) {
+		size_t bh_written;
 
-	if (old_size < pos)
-		pagecache_isize_extended(iter->inode, old_size, pos);
+		bh_written = block_write_end(NULL, iter->inode->i_mapping, pos,
+					len, copied, &folio->page, NULL);
+		WARN_ON_ONCE(bh_written != copied && bh_written != 0);
+		return bh_written == copied;
+	}
 
-	return written == copied;
+	return __iomap_write_end(iter->inode, pos, len, copied, folio);
 }
 
 static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
@@ -917,6 +920,7 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 
 	do {
 		struct folio *folio;
+		loff_t old_size;
 		size_t offset;		/* Offset into folio */
 		size_t bytes;		/* Bytes to write to folio */
 		size_t copied;		/* Bytes copied from user */
@@ -968,6 +972,23 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 		written = iomap_write_end(iter, pos, bytes, copied, folio) ?
 			  copied : 0;
 
+		/*
+		 * Update the in-memory inode size after copying the data into
+		 * the page cache.  It's up to the file system to write the
+		 * updated size to disk, preferably after I/O completion so that
+		 * no stale data is exposed.  Only once that's done can we
+		 * unlock and release the folio.
+		 */
+		old_size = iter->inode->i_size;
+		if (pos + written > old_size) {
+			i_size_write(iter->inode, pos + written);
+			iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
+		}
+		__iomap_put_folio(iter, pos, written, folio);
+
+		if (old_size < pos)
+			pagecache_isize_extended(iter->inode, old_size, pos);
+
 		cond_resched();
 		if (unlikely(written == 0)) {
 			/*
@@ -1338,6 +1359,7 @@ static loff_t iomap_unshare_iter(struct iomap_iter *iter)
 			bytes = folio_size(folio) - offset;
 
 		ret = iomap_write_end(iter, pos, bytes, bytes, folio);
+		__iomap_put_folio(iter, pos, bytes, folio);
 		if (WARN_ON_ONCE(!ret))
 			return -EIO;
 
@@ -1403,6 +1425,7 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
 		folio_mark_accessed(folio);
 
 		ret = iomap_write_end(iter, pos, bytes, bytes, folio);
+		__iomap_put_folio(iter, pos, bytes, folio);
 		if (WARN_ON_ONCE(!ret))
 			return -EIO;
 

fs/xfs/xfs_iops.c

@@ -17,6 +17,8 @@
 #include "xfs_da_btree.h"
 #include "xfs_attr.h"
 #include "xfs_trans.h"
+#include "xfs_trans_space.h"
+#include "xfs_bmap_btree.h"
 #include "xfs_trace.h"
 #include "xfs_icache.h"
 #include "xfs_symlink.h"
@@ -811,6 +813,7 @@ xfs_setattr_size(
 	struct xfs_trans	*tp;
 	int			error;
 	uint			lock_flags = 0;
+	uint			resblks = 0;
 	bool			did_zeroing = false;
 
 	xfs_assert_ilocked(ip, XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL);
@@ -917,7 +920,17 @@ xfs_setattr_size(
 			return error;
 	}
 
-	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0, 0, 0, &tp);
+	/*
+	 * For realtime inode with more than one block rtextsize, we need the
+	 * block reservation for bmap btree block allocations/splits that can
+	 * happen since it could split the tail written extent and convert the
+	 * right beyond EOF one to unwritten.
+	 */
+	if (xfs_inode_has_bigrtalloc(ip))
+		resblks = XFS_DIOSTRAT_SPACE_RES(mp, 0);
+
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, resblks,
+				0, 0, &tp);
 	if (error)
 		return error;