[PATCH RFC 11/11] fs: move generic_file_write_iter() family to fs/read_write.c

[Tal Zussman <tz2294@columbia.edu>]

Move the VFS-level generic write path out of mm/filemap.c into
fs/read_write.c next to the just-relocated read path:

  - generic_file_write_iter()
  - __generic_file_write_iter()
  - generic_file_direct_write()
  - generic_perform_write()
  - kiocb_invalidate_pages()
  - kiocb_invalidate_post_direct_write()
  - dio_warn_stale_pagecache()

The kiocb_invalidate_* prototypes move from <linux/pagemap.h> to
<linux/fs.h>, joining kiocb_write_and_wait() and the other generic
read/write declarations. Drop extern from the prototypes of all
five generic_file_* declarations in <linux/fs.h>. Reflow the
generic_file_direct_write() definition to fit on one line.

Signed-off-by: Tal Zussman <tz2294@columbia.edu>
---
 fs/read_write.c         | 276 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h      |   8 +-
 include/linux/pagemap.h |   2 -
 mm/filemap.c            | 277 ------------------------------------------------
 4 files changed, 281 insertions(+), 282 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 59ceea85c163..cea5f79fdacf 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1071,6 +1071,282 @@ ssize_t generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 }
 EXPORT_SYMBOL(generic_file_read_iter);
 
+int kiocb_invalidate_pages(struct kiocb *iocb, size_t count)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+
+	return filemap_invalidate_pages(mapping, iocb->ki_pos,
+					iocb->ki_pos + count - 1,
+					iocb->ki_flags & IOCB_NOWAIT);
+}
+EXPORT_SYMBOL_GPL(kiocb_invalidate_pages);
+
+/*
+ * Warn about a page cache invalidation failure during a direct I/O write.
+ */
+static void dio_warn_stale_pagecache(struct file *filp)
+{
+	static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
+	char pathname[128];
+	char *path;
+
+	errseq_set(&filp->f_mapping->wb_err, -EIO);
+	if (__ratelimit(&_rs)) {
+		path = file_path(filp, pathname, sizeof(pathname));
+		if (IS_ERR(path))
+			path = "(unknown)";
+		pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
+		pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
+			current->comm);
+	}
+}
+
+void kiocb_invalidate_post_direct_write(struct kiocb *iocb, size_t count)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+
+	if (mapping->nrpages &&
+	    invalidate_inode_pages2_range(mapping,
+			iocb->ki_pos >> PAGE_SHIFT,
+			(iocb->ki_pos + count - 1) >> PAGE_SHIFT))
+		dio_warn_stale_pagecache(iocb->ki_filp);
+}
+
+ssize_t generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	size_t write_len = iov_iter_count(from);
+	ssize_t written;
+
+	/*
+	 * If a page can not be invalidated, return 0 to fall back
+	 * to buffered write.
+	 */
+	written = kiocb_invalidate_pages(iocb, write_len);
+	if (written) {
+		if (written == -EBUSY)
+			return 0;
+		return written;
+	}
+
+	written = mapping->a_ops->direct_IO(iocb, from);
+
+	/*
+	 * Finally, try again to invalidate clean pages which might have been
+	 * cached by non-direct readahead, or faulted in by get_user_pages()
+	 * if the source of the write was an mmap'ed region of the file
+	 * we're writing.  Either one is a pretty crazy thing to do,
+	 * so we don't support it 100%.  If this invalidation
+	 * fails, tough, the write still worked...
+	 *
+	 * Most of the time we do not need this since dio_complete() will do
+	 * the invalidation for us. However there are some file systems that
+	 * do not end up with dio_complete() being called, so let's not break
+	 * them by removing it completely.
+	 *
+	 * Noticeable example is a blkdev_direct_IO().
+	 *
+	 * Skip invalidation for async writes or if mapping has no pages.
+	 */
+	if (written > 0) {
+		struct inode *inode = mapping->host;
+		loff_t pos = iocb->ki_pos;
+
+		kiocb_invalidate_post_direct_write(iocb, written);
+		pos += written;
+		write_len -= written;
+		if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
+			i_size_write(inode, pos);
+			mark_inode_dirty(inode);
+		}
+		iocb->ki_pos = pos;
+	}
+	if (written != -EIOCBQUEUED)
+		iov_iter_revert(from, write_len - iov_iter_count(from));
+	return written;
+}
+EXPORT_SYMBOL(generic_file_direct_write);
+
+ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
+{
+	struct file *file = iocb->ki_filp;
+	loff_t pos = iocb->ki_pos;
+	struct address_space *mapping = file->f_mapping;
+	const struct address_space_operations *a_ops = mapping->a_ops;
+	size_t chunk = mapping_max_folio_size(mapping);
+	long status = 0;
+	ssize_t written = 0;
+
+	do {
+		struct folio *folio;
+		size_t offset;		/* Offset into folio */
+		size_t bytes;		/* Bytes to write to folio */
+		size_t copied;		/* Bytes copied from user */
+		void *fsdata = NULL;
+
+		bytes = iov_iter_count(i);
+retry:
+		offset = pos & (chunk - 1);
+		bytes = min(chunk - offset, bytes);
+		balance_dirty_pages_ratelimited(mapping);
+
+		if (fatal_signal_pending(current)) {
+			status = -EINTR;
+			break;
+		}
+
+		status = a_ops->write_begin(iocb, mapping, pos, bytes,
+						&folio, &fsdata);
+		if (unlikely(status < 0))
+			break;
+
+		offset = offset_in_folio(folio, pos);
+		if (bytes > folio_size(folio) - offset)
+			bytes = folio_size(folio) - offset;
+
+		if (mapping_writably_mapped(mapping))
+			flush_dcache_folio(folio);
+
+		/*
+		 * Faults here on mmap()s can recurse into arbitrary
+		 * filesystem code. Lots of locks are held that can
+		 * deadlock. Use an atomic copy to avoid deadlocking
+		 * in page fault handling.
+		 */
+		copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
+		flush_dcache_folio(folio);
+
+		status = a_ops->write_end(iocb, mapping, pos, bytes, copied,
+						folio, fsdata);
+		if (unlikely(status != copied)) {
+			iov_iter_revert(i, copied - max(status, 0L));
+			if (unlikely(status < 0))
+				break;
+		}
+		cond_resched();
+
+		if (unlikely(status == 0)) {
+			/*
+			 * A short copy made ->write_end() reject the
+			 * thing entirely.  Might be memory poisoning
+			 * halfway through, might be a race with munmap,
+			 * might be severe memory pressure.
+			 */
+			if (chunk > PAGE_SIZE)
+				chunk /= 2;
+			if (copied) {
+				bytes = copied;
+				goto retry;
+			}
+
+			/*
+			 * 'folio' is now unlocked and faults on it can be
+			 * handled. Ensure forward progress by trying to
+			 * fault it in now.
+			 */
+			if (fault_in_iov_iter_readable(i, bytes) == bytes) {
+				status = -EFAULT;
+				break;
+			}
+		} else {
+			pos += status;
+			written += status;
+		}
+	} while (iov_iter_count(i));
+
+	if (!written)
+		return status;
+	iocb->ki_pos += written;
+	return written;
+}
+EXPORT_SYMBOL(generic_perform_write);
+
+/**
+ * __generic_file_write_iter - write data to a file
+ * @iocb:	IO state structure (file, offset, etc.)
+ * @from:	iov_iter with data to write
+ *
+ * This function does all the work needed for actually writing data to a
+ * file. It does all basic checks, removes SUID from the file, updates
+ * modification times and calls proper subroutines depending on whether we
+ * do direct IO or a standard buffered write.
+ *
+ * It expects i_rwsem to be grabbed unless we work on a block device or similar
+ * object which does not need locking at all.
+ *
+ * This function does *not* take care of syncing data in case of O_SYNC write.
+ * A caller has to handle it. This is mainly due to the fact that we want to
+ * avoid syncing under i_rwsem.
+ *
+ * Return:
+ * * number of bytes written, even for truncated writes
+ * * negative error code if no data has been written at all
+ */
+ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
+	ssize_t ret;
+
+	ret = file_remove_privs(file);
+	if (ret)
+		return ret;
+
+	ret = file_update_time(file);
+	if (ret)
+		return ret;
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		ret = generic_file_direct_write(iocb, from);
+		/*
+		 * If the write stopped short of completing, fall back to
+		 * buffered writes.  Some filesystems do this for writes to
+		 * holes, for example.  For DAX files, a buffered write will
+		 * not succeed (even if it did, DAX does not handle dirty
+		 * page-cache pages correctly).
+		 */
+		if (ret < 0 || !iov_iter_count(from) || IS_DAX(inode))
+			return ret;
+		return direct_write_fallback(iocb, from, ret,
+				generic_perform_write(iocb, from));
+	}
+
+	return generic_perform_write(iocb, from);
+}
+EXPORT_SYMBOL(__generic_file_write_iter);
+
+/**
+ * generic_file_write_iter - write data to a file
+ * @iocb:	IO state structure
+ * @from:	iov_iter with data to write
+ *
+ * This is a wrapper around __generic_file_write_iter() to be used by most
+ * filesystems. It takes care of syncing the file in case of O_SYNC file
+ * and acquires i_rwsem as needed.
+ * Return:
+ * * negative error code if no data has been written at all of
+ *   vfs_fsync_range() failed for a synchronous write
+ * * number of bytes written, even for truncated writes
+ */
+ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct inode *inode = file->f_mapping->host;
+	ssize_t ret;
+
+	inode_lock(inode);
+	ret = generic_write_checks(iocb, from);
+	if (ret > 0)
+		ret = __generic_file_write_iter(iocb, from);
+	inode_unlock(inode);
+
+	if (ret > 0)
+		ret = generic_write_sync(iocb, ret);
+	return ret;
+}
+EXPORT_SYMBOL(generic_file_write_iter);
+
 static ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
 			 unsigned long vlen, loff_t *pos, rwf_t flags)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c0151ced8e7a..6cfb9e46bc37 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3057,9 +3057,11 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *to,
 		ssize_t already_read);
 ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *);
 int kiocb_write_and_wait(struct kiocb *iocb, size_t count);
-extern ssize_t __generic_file_write_iter(struct kiocb *, struct iov_iter *);
-extern ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
-extern ssize_t generic_file_direct_write(struct kiocb *, struct iov_iter *);
+int kiocb_invalidate_pages(struct kiocb *iocb, size_t count);
+void kiocb_invalidate_post_direct_write(struct kiocb *iocb, size_t count);
+ssize_t __generic_file_write_iter(struct kiocb *, struct iov_iter *);
+ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
+ssize_t generic_file_direct_write(struct kiocb *, struct iov_iter *);
 ssize_t generic_perform_write(struct kiocb *, struct iov_iter *);
 ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
 		ssize_t direct_written, ssize_t buffered_written);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 46cefd552a51..b7c2dc8076ab 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -31,8 +31,6 @@ static inline void invalidate_remote_inode(struct inode *inode)
 int invalidate_inode_pages2(struct address_space *mapping);
 int invalidate_inode_pages2_range(struct address_space *mapping,
 		pgoff_t start, pgoff_t end);
-int kiocb_invalidate_pages(struct kiocb *iocb, size_t count);
-void kiocb_invalidate_post_direct_write(struct kiocb *iocb, size_t count);
 int filemap_invalidate_pages(struct address_space *mapping,
 			     loff_t pos, loff_t end, bool nowait);
 
diff --git a/mm/filemap.c b/mm/filemap.c
index db7c53cd681b..284c0296a011 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2276,17 +2276,6 @@ int filemap_invalidate_pages(struct address_space *mapping,
 					     end >> PAGE_SHIFT);
 }
 
-int kiocb_invalidate_pages(struct kiocb *iocb, size_t count)
-{
-	struct address_space *mapping = iocb->ki_filp->f_mapping;
-
-	return filemap_invalidate_pages(mapping, iocb->ki_pos,
-					iocb->ki_pos + count - 1,
-					iocb->ki_flags & IOCB_NOWAIT);
-}
-EXPORT_SYMBOL_GPL(kiocb_invalidate_pages);
-
-
 /*
  * Splice subpages from a folio into a pipe.
  */
@@ -3500,272 +3489,6 @@ struct page *read_cache_page_gfp(struct address_space *mapping,
 }
 EXPORT_SYMBOL(read_cache_page_gfp);
 
-/*
- * Warn about a page cache invalidation failure during a direct I/O write.
- */
-static void dio_warn_stale_pagecache(struct file *filp)
-{
-	static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
-	char pathname[128];
-	char *path;
-
-	errseq_set(&filp->f_mapping->wb_err, -EIO);
-	if (__ratelimit(&_rs)) {
-		path = file_path(filp, pathname, sizeof(pathname));
-		if (IS_ERR(path))
-			path = "(unknown)";
-		pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
-		pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
-			current->comm);
-	}
-}
-
-void kiocb_invalidate_post_direct_write(struct kiocb *iocb, size_t count)
-{
-	struct address_space *mapping = iocb->ki_filp->f_mapping;
-
-	if (mapping->nrpages &&
-	    invalidate_inode_pages2_range(mapping,
-			iocb->ki_pos >> PAGE_SHIFT,
-			(iocb->ki_pos + count - 1) >> PAGE_SHIFT))
-		dio_warn_stale_pagecache(iocb->ki_filp);
-}
-
-ssize_t
-generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
-{
-	struct address_space *mapping = iocb->ki_filp->f_mapping;
-	size_t write_len = iov_iter_count(from);
-	ssize_t written;
-
-	/*
-	 * If a page can not be invalidated, return 0 to fall back
-	 * to buffered write.
-	 */
-	written = kiocb_invalidate_pages(iocb, write_len);
-	if (written) {
-		if (written == -EBUSY)
-			return 0;
-		return written;
-	}
-
-	written = mapping->a_ops->direct_IO(iocb, from);
-
-	/*
-	 * Finally, try again to invalidate clean pages which might have been
-	 * cached by non-direct readahead, or faulted in by get_user_pages()
-	 * if the source of the write was an mmap'ed region of the file
-	 * we're writing.  Either one is a pretty crazy thing to do,
-	 * so we don't support it 100%.  If this invalidation
-	 * fails, tough, the write still worked...
-	 *
-	 * Most of the time we do not need this since dio_complete() will do
-	 * the invalidation for us. However there are some file systems that
-	 * do not end up with dio_complete() being called, so let's not break
-	 * them by removing it completely.
-	 *
-	 * Noticeable example is a blkdev_direct_IO().
-	 *
-	 * Skip invalidation for async writes or if mapping has no pages.
-	 */
-	if (written > 0) {
-		struct inode *inode = mapping->host;
-		loff_t pos = iocb->ki_pos;
-
-		kiocb_invalidate_post_direct_write(iocb, written);
-		pos += written;
-		write_len -= written;
-		if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
-			i_size_write(inode, pos);
-			mark_inode_dirty(inode);
-		}
-		iocb->ki_pos = pos;
-	}
-	if (written != -EIOCBQUEUED)
-		iov_iter_revert(from, write_len - iov_iter_count(from));
-	return written;
-}
-EXPORT_SYMBOL(generic_file_direct_write);
-
-ssize_t generic_perform_write(struct kiocb *iocb, struct iov_iter *i)
-{
-	struct file *file = iocb->ki_filp;
-	loff_t pos = iocb->ki_pos;
-	struct address_space *mapping = file->f_mapping;
-	const struct address_space_operations *a_ops = mapping->a_ops;
-	size_t chunk = mapping_max_folio_size(mapping);
-	long status = 0;
-	ssize_t written = 0;
-
-	do {
-		struct folio *folio;
-		size_t offset;		/* Offset into folio */
-		size_t bytes;		/* Bytes to write to folio */
-		size_t copied;		/* Bytes copied from user */
-		void *fsdata = NULL;
-
-		bytes = iov_iter_count(i);
-retry:
-		offset = pos & (chunk - 1);
-		bytes = min(chunk - offset, bytes);
-		balance_dirty_pages_ratelimited(mapping);
-
-		if (fatal_signal_pending(current)) {
-			status = -EINTR;
-			break;
-		}
-
-		status = a_ops->write_begin(iocb, mapping, pos, bytes,
-						&folio, &fsdata);
-		if (unlikely(status < 0))
-			break;
-
-		offset = offset_in_folio(folio, pos);
-		if (bytes > folio_size(folio) - offset)
-			bytes = folio_size(folio) - offset;
-
-		if (mapping_writably_mapped(mapping))
-			flush_dcache_folio(folio);
-
-		/*
-		 * Faults here on mmap()s can recurse into arbitrary
-		 * filesystem code. Lots of locks are held that can
-		 * deadlock. Use an atomic copy to avoid deadlocking
-		 * in page fault handling.
-		 */
-		copied = copy_folio_from_iter_atomic(folio, offset, bytes, i);
-		flush_dcache_folio(folio);
-
-		status = a_ops->write_end(iocb, mapping, pos, bytes, copied,
-						folio, fsdata);
-		if (unlikely(status != copied)) {
-			iov_iter_revert(i, copied - max(status, 0L));
-			if (unlikely(status < 0))
-				break;
-		}
-		cond_resched();
-
-		if (unlikely(status == 0)) {
-			/*
-			 * A short copy made ->write_end() reject the
-			 * thing entirely.  Might be memory poisoning
-			 * halfway through, might be a race with munmap,
-			 * might be severe memory pressure.
-			 */
-			if (chunk > PAGE_SIZE)
-				chunk /= 2;
-			if (copied) {
-				bytes = copied;
-				goto retry;
-			}
-
-			/*
-			 * 'folio' is now unlocked and faults on it can be
-			 * handled. Ensure forward progress by trying to
-			 * fault it in now.
-			 */
-			if (fault_in_iov_iter_readable(i, bytes) == bytes) {
-				status = -EFAULT;
-				break;
-			}
-		} else {
-			pos += status;
-			written += status;
-		}
-	} while (iov_iter_count(i));
-
-	if (!written)
-		return status;
-	iocb->ki_pos += written;
-	return written;
-}
-EXPORT_SYMBOL(generic_perform_write);
-
-/**
- * __generic_file_write_iter - write data to a file
- * @iocb:	IO state structure (file, offset, etc.)
- * @from:	iov_iter with data to write
- *
- * This function does all the work needed for actually writing data to a
- * file. It does all basic checks, removes SUID from the file, updates
- * modification times and calls proper subroutines depending on whether we
- * do direct IO or a standard buffered write.
- *
- * It expects i_rwsem to be grabbed unless we work on a block device or similar
- * object which does not need locking at all.
- *
- * This function does *not* take care of syncing data in case of O_SYNC write.
- * A caller has to handle it. This is mainly due to the fact that we want to
- * avoid syncing under i_rwsem.
- *
- * Return:
- * * number of bytes written, even for truncated writes
- * * negative error code if no data has been written at all
- */
-ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
-{
-	struct file *file = iocb->ki_filp;
-	struct address_space *mapping = file->f_mapping;
-	struct inode *inode = mapping->host;
-	ssize_t ret;
-
-	ret = file_remove_privs(file);
-	if (ret)
-		return ret;
-
-	ret = file_update_time(file);
-	if (ret)
-		return ret;
-
-	if (iocb->ki_flags & IOCB_DIRECT) {
-		ret = generic_file_direct_write(iocb, from);
-		/*
-		 * If the write stopped short of completing, fall back to
-		 * buffered writes.  Some filesystems do this for writes to
-		 * holes, for example.  For DAX files, a buffered write will
-		 * not succeed (even if it did, DAX does not handle dirty
-		 * page-cache pages correctly).
-		 */
-		if (ret < 0 || !iov_iter_count(from) || IS_DAX(inode))
-			return ret;
-		return direct_write_fallback(iocb, from, ret,
-				generic_perform_write(iocb, from));
-	}
-
-	return generic_perform_write(iocb, from);
-}
-EXPORT_SYMBOL(__generic_file_write_iter);
-
-/**
- * generic_file_write_iter - write data to a file
- * @iocb:	IO state structure
- * @from:	iov_iter with data to write
- *
- * This is a wrapper around __generic_file_write_iter() to be used by most
- * filesystems. It takes care of syncing the file in case of O_SYNC file
- * and acquires i_rwsem as needed.
- * Return:
- * * negative error code if no data has been written at all of
- *   vfs_fsync_range() failed for a synchronous write
- * * number of bytes written, even for truncated writes
- */
-ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
-{
-	struct file *file = iocb->ki_filp;
-	struct inode *inode = file->f_mapping->host;
-	ssize_t ret;
-
-	inode_lock(inode);
-	ret = generic_write_checks(iocb, from);
-	if (ret > 0)
-		ret = __generic_file_write_iter(iocb, from);
-	inode_unlock(inode);
-
-	if (ret > 0)
-		ret = generic_write_sync(iocb, ret);
-	return ret;
-}
-EXPORT_SYMBOL(generic_file_write_iter);
 
 /**
  * filemap_release_folio() - Release fs-specific metadata on a folio.

-- 
2.39.5