[PATCH 5/5] ext4: implement FALLOC_FL_ZEROINIT_RANGE

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

Implement this new fallocate mode so that persistent memory users can,
upon receipt of a pmem poison notification, cause the pmem to be
reinitialized to a known value (zero) and clear any hardware poison
state that might be lurking.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/ext4/extents.c           |   93 +++++++++++++++++++++++++++++++++++++++++++
 include/trace/events/ext4.h |    7 +++
 2 files changed, 99 insertions(+), 1 deletion(-)


diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c0de30f25185..c345002e2da6 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -29,6 +29,7 @@
 #include <linux/fiemap.h>
 #include <linux/backing-dev.h>
 #include <linux/iomap.h>
+#include <linux/dax.h>
 #include "ext4_jbd2.h"
 #include "ext4_extents.h"
 #include "xattr.h"
@@ -4475,6 +4476,90 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len);
 
 static int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len);
 
+static long ext4_zeroinit_range(struct file *file, loff_t offset, loff_t len)
+{
+	struct inode *inode = file_inode(file);
+	struct address_space *mapping = inode->i_mapping;
+	handle_t *handle = NULL;
+	loff_t end = offset + len;
+	long ret;
+
+	trace_ext4_zeroinit_range(inode, offset, len,
+			FALLOC_FL_ZEROINIT_RANGE | FALLOC_FL_KEEP_SIZE);
+
+	/* We don't support data=journal mode */
+	if (ext4_should_journal_data(inode))
+		return -EOPNOTSUPP;
+
+	inode_lock(inode);
+
+	/*
+	 * Indirect files do not support unwritten extents
+	 */
+	if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
+		ret = -EOPNOTSUPP;
+		goto out_mutex;
+	}
+
+	/* Wait all existing dio workers, newcomers will block on i_mutex */
+	inode_dio_wait(inode);
+
+	/*
+	 * Prevent page faults from reinstantiating pages we have released from
+	 * page cache.
+	 */
+	filemap_invalidate_lock(mapping);
+
+	ret = ext4_break_layouts(inode);
+	if (ret)
+		goto out_mmap;
+
+	/* Now release the pages and zero block aligned part of pages */
+	truncate_pagecache_range(inode, offset, end - 1);
+	inode->i_mtime = inode->i_ctime = current_time(inode);
+
+	if (IS_DAX(inode))
+		ret = dax_zeroinit_range(inode, offset, len,
+				&ext4_iomap_report_ops);
+	else
+		ret = iomap_zeroout_range(inode, offset, len,
+				&ext4_iomap_report_ops);
+	if (ret == -ECANCELED)
+		ret = -EOPNOTSUPP;
+	if (ret)
+		goto out_mmap;
+
+	/*
+	 * In worst case we have to writeout two nonadjacent unwritten
+	 * blocks and update the inode
+	 */
+	handle = ext4_journal_start(inode, EXT4_HT_MISC, 1);
+	if (IS_ERR(handle)) {
+		ret = PTR_ERR(handle);
+		ext4_std_error(inode->i_sb, ret);
+		goto out_mmap;
+	}
+
+	inode->i_mtime = inode->i_ctime = current_time(inode);
+	ret = ext4_mark_inode_dirty(handle, inode);
+	if (unlikely(ret))
+		goto out_handle;
+	ext4_fc_track_range(handle, inode, offset >> inode->i_sb->s_blocksize_bits,
+			(offset + len - 1) >> inode->i_sb->s_blocksize_bits);
+	ext4_update_inode_fsync_trans(handle, inode, 1);
+
+	if (file->f_flags & O_SYNC)
+		ext4_handle_sync(handle);
+
+out_handle:
+	ext4_journal_stop(handle);
+out_mmap:
+	filemap_invalidate_unlock(mapping);
+out_mutex:
+	inode_unlock(inode);
+	return ret;
+}
+
 static long ext4_zero_range(struct file *file, loff_t offset,
 			    loff_t len, int mode)
 {
@@ -4659,7 +4744,7 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	/* Return error if mode is not supported */
 	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
 		     FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |
-		     FALLOC_FL_INSERT_RANGE))
+		     FALLOC_FL_INSERT_RANGE | FALLOC_FL_ZEROINIT_RANGE))
 		return -EOPNOTSUPP;
 
 	ext4_fc_start_update(inode);
@@ -4687,6 +4772,12 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 		ret = ext4_zero_range(file, offset, len, mode);
 		goto exit;
 	}
+
+	if (mode & FALLOC_FL_ZEROINIT_RANGE) {
+		ret = ext4_zeroinit_range(file, offset, len);
+		goto exit;
+	}
+
 	trace_ext4_fallocate_enter(inode, offset, len, mode);
 	lblk = offset >> blkbits;
 
diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index 0ea36b2b0662..282f1208067f 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -1407,6 +1407,13 @@ DEFINE_EVENT(ext4__fallocate_mode, ext4_zero_range,
 	TP_ARGS(inode, offset, len, mode)
 );
 
+DEFINE_EVENT(ext4__fallocate_mode, ext4_zeroinit_range,
+
+	TP_PROTO(struct inode *inode, loff_t offset, loff_t len, int mode),
+
+	TP_ARGS(inode, offset, len, mode)
+);
+
 TRACE_EVENT(ext4_fallocate_exit,
 	TP_PROTO(struct inode *inode, loff_t offset,
 		 unsigned int max_blocks, int ret),