linux-kernel - Re: [PATCH v2] f2fs: allocate blocks for pinned file

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Message-ID: <20190628153614.GA27114@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Fri, 28 Jun 2019 08:36:14 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH v2] f2fs: allocate blocks for pinned file

This patch allows fallocate to allocate physical blocks for pinned file.

Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
 Documentation/filesystems/f2fs.txt | 25 +++++++++++++++++++++++++
 fs/f2fs/file.c                     |  7 ++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index bebd1be3ba49..496fa28b2492 100644
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -804,3 +804,28 @@ WRITE_LIFE_NOT_SET    WARM_DATA                WRITE_LIFE_NOT_SET
 WRITE_LIFE_NONE       "                        WRITE_LIFE_NONE
 WRITE_LIFE_MEDIUM     "                        WRITE_LIFE_MEDIUM
 WRITE_LIFE_LONG       "                        WRITE_LIFE_LONG
+
+Fallocate(2) Policy
+-------------------
+
+The default policy follows the below posix rule.
+
+Allocating disk space
+    The default operation (i.e., mode is zero) of fallocate() allocates
+    the disk space within the range specified by offset and len.  The
+    file size (as reported by stat(2)) will be changed if offset+len is
+    greater than the file size.  Any subregion within the range specified
+    by offset and len that did not contain data before the call will be
+    initialized to zero.  This default behavior closely resembles the
+    behavior of the posix_fallocate(3) library function, and is intended
+    as a method of optimally implementing that function.
+
+However, once F2FS receives ioctl(fd, F2FS_IOC_SET_PIN_FILE) in prior to
+fallocate(fd, DEFAULT_MODE), it allocates on-disk blocks addressess having
+zero or random data, which is useful to the below scenario where:
+ 1. create(fd)
+ 2. ioctl(fd, F2FS_IOC_SET_PIN_FILE)
+ 3. fallocate(fd, 0, 0, size)
+ 4. address = fibmap(fd, offset)
+ 5. open(blkdev)
+ 6. write(blkdev, address)
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index e7c368db8185..cdfd4338682d 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1528,7 +1528,12 @@ static int expand_inode_data(struct inode *inode, loff_t offset,
 	if (off_end)
 		map.m_len++;
 
-	err = f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_AIO);
+	if (f2fs_is_pinned_file(inode))
+		map.m_seg_type = CURSEG_COLD_DATA;
+
+	err = f2fs_map_blocks(inode, &map, 1, (f2fs_is_pinned_file(inode) ?
+						F2FS_GET_BLOCK_PRE_DIO :
+						F2FS_GET_BLOCK_PRE_AIO));
 	if (err) {
 		pgoff_t last_off;
 
-- 
2.19.0.605.g01d371f741-goog