linux-ext4 - [PATCH 4/5] fuse2fs: allow use of direct io for disk access

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Message-ID: <174553065581.1161238.969038742323698265.stgit@frogsfrogsfrogs>
Date: Thu, 24 Apr 2025 14:46:33 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: linux-ext4@...r.kernel.org
Subject: [PATCH 4/5] fuse2fs: allow use of direct io for disk access

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

Allow users to ask for O_DIRECT for disk accesses so that block device
writes won't be throttled.  This should improve latency, but will put
a lot more pressure on the disk cache.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 misc/fuse2fs.1.in |    3 +++
 misc/fuse2fs.c    |    5 +++++
 2 files changed, 8 insertions(+)


diff --git a/misc/fuse2fs.1.in b/misc/fuse2fs.1.in
index 517c67ff719911..43678a1c1971c5 100644
--- a/misc/fuse2fs.1.in
+++ b/misc/fuse2fs.1.in
@@ -62,6 +62,9 @@ .SS "fuse2fs options:"
 Note that these options can still be overridden (e.g.
 .I nosuid
 ) later.
+.TP
+.BR -o direct
+Use O_DIRECT to access the block device.
 .SS "FUSE options:"
 .TP
 \fB-d -o\fR debug
diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 7f1e7556b9204e..6aac84a2b4340b 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -158,6 +158,7 @@ struct fuse2fs {
 	int alloc_all_blocks;
 	int norecovery;
 	int kernel;
+	int directio;
 	unsigned long offset;
 	unsigned int next_generation;
 };
@@ -3776,6 +3777,7 @@ static struct fuse_opt fuse2fs_opts[] = {
 	FUSE2FS_OPT("noload",		norecovery,		1),
 	FUSE2FS_OPT("offset=%lu",	offset,			0),
 	FUSE2FS_OPT("kernel",		kernel,			1),
+	FUSE2FS_OPT("directio",		directio,		1),
 
 	FUSE_OPT_KEY("acl",		FUSE2FS_IGNORED),
 	FUSE_OPT_KEY("user_xattr",	FUSE2FS_IGNORED),
@@ -3824,6 +3826,7 @@ static int fuse2fs_opt_proc(void *data, const char *arg,
 	"    -o fuse2fs_debug       enable fuse2fs debugging\n"
 	"    -o kernel              run this as if it were the kernel, which sets:\n"
 	"                           allow_others,default_permissions,suid,dev\n"
+	"    -o directio            use O_DIRECT to read and write the disk\n"
 	"\n",
 			outargs->argv[0]);
 		if (key == FUSE2FS_HELPFULL) {
@@ -3929,6 +3932,8 @@ int main(int argc, char *argv[])
 	ret = 2;
 	char options[50];
 	sprintf(options, "offset=%lu", fctx.offset);
+	if (fctx.directio)
+		flags |= EXT2_FLAG_DIRECT_IO;
 	err = ext2fs_open2(fctx.device, options, flags, 0, 0, unix_io_manager,
 			   &global_fs);
 	if (err) {