[RFC PATCH 7/7] f2fs: support STATX_IOALIGN

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

Add support for STATX_IOALIGN to f2fs, so that I/O alignment information
is exposed to userspace in a consistent and easy-to-use way.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/f2fs/file.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 9cc985258f17e..334d363a7b8c5 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -835,6 +835,21 @@ static bool f2fs_force_buffered_io(struct inode *inode)
 	return false;
 }
 
+/* Return the maximum value of io_opt across all the filesystem's devices. */
+static unsigned int f2fs_max_io_opt(struct inode *inode)
+{
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	int io_opt = 0;
+	int i;
+
+	if (!f2fs_is_multi_device(sbi))
+		return bdev_io_opt(sbi->sb->s_bdev);
+
+	for (i = 0; i < sbi->s_ndevs; i++)
+		io_opt = max(io_opt, bdev_io_opt(FDEV(i).bdev));
+	return io_opt;
+}
+
 int f2fs_getattr(struct user_namespace *mnt_userns, const struct path *path,
 		 struct kstat *stat, u32 request_mask, unsigned int query_flags)
 {
@@ -851,6 +866,22 @@ int f2fs_getattr(struct user_namespace *mnt_userns, const struct path *path,
 		stat->btime.tv_nsec = fi->i_crtime.tv_nsec;
 	}
 
+	/*
+	 * Return the I/O alignment information if requested.  We only return
+	 * this information when requested, since on encrypted files it might
+	 * take a fair bit of work to get if the file wasn't opened recently.
+	 */
+	if ((request_mask & STATX_IOALIGN) && S_ISREG(inode->i_mode)) {
+		unsigned int bsize = i_blocksize(inode);
+
+		stat->result_mask |= STATX_IOALIGN;
+		if (!f2fs_force_buffered_io(inode)) {
+			stat->mem_align_dio = bsize;
+			stat->offset_align_dio = bsize;
+		}
+		stat->offset_align_optimal = max(f2fs_max_io_opt(inode), bsize);
+	}
+
 	flags = fi->i_flags;
 	if (flags & F2FS_COMPR_FL)
 		stat->attributes |= STATX_ATTR_COMPRESSED;
-- 
2.35.1