linux-ext4 - [RFC 1/7] iomap: Don't fall back to buffered write if the write is atomic

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Message-Id: <09ec4c88b565c85dee91eccf6e894a0c047d9e69.1701339358.git.ojaswin@linux.ibm.com>
Date: Thu, 30 Nov 2023 19:23:09 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Cc: Ritesh Harjani <ritesh.list@...il.com>, linux-kernel@...r.kernel.org,
        "Darrick J . Wong" <djwong@...nel.org>, linux-block@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        John Garry <john.g.garry@...cle.com>, dchinner@...hat.com
Subject: [RFC 1/7] iomap: Don't fall back to buffered write if the write is atomic

Currently, iomap only supports atomic writes for direct IOs and there is
no guarantees that a buffered IO will be atomic. Hence, if the user has
explicitly requested the direct write to be atomic and there's a
failure, return -EIO instead of falling back to buffered IO.

Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
---
 fs/iomap/direct-io.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 6ef25e26f1a1..3e7cd9bc8f4d 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -662,7 +662,13 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 			if (ret != -EAGAIN) {
 				trace_iomap_dio_invalidate_fail(inode, iomi.pos,
 								iomi.len);
-				ret = -ENOTBLK;
+				/*
+				 * if this write was supposed to be atomic,
+				 * return the err rather than trying to fall
+				 * back to buffered IO.
+				 */
+				if (!atomic_write)
+					ret = -ENOTBLK;
 			}
 			goto out_free_dio;
 		}
-- 
2.39.3