linux-ext4 - [PATCH 12/16] fuse2fs: don't zero bytes in punch hole

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Message-ID: <174787198650.1484996.5639277239335638587.stgit@frogsfrogsfrogs>
Date: Wed, 21 May 2025 17:13:58 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: John@...ves.net, linux-ext4@...r.kernel.org, miklos@...redi.hu,
 joannelkoong@...il.com, bernd@...ernd.com, linux-fsdevel@...r.kernel.org
Subject: [PATCH 12/16] fuse2fs: don't zero bytes in punch hole

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

When iomap is in use for the pagecache, it will take care of zeroing the
unaligned parts of punched out regions so we don't have to do it
ourselves.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 misc/fuse2fs.c |   32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)


diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index fe6d97324c1f57..aeb2b6fbc28401 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -152,6 +152,7 @@ enum fuse2fs_iomap_state {
 	IOMAP_DISABLED,
 	IOMAP_UNKNOWN,
 	IOMAP_ENABLED,
+	IOMAP_FILEIO,	/* enabled and does all file data block IO */
 };
 #endif
 
@@ -1040,6 +1041,7 @@ static errcode_t confirm_iomap(struct fuse_conn_info *conn, struct fuse2fs *ff)
 		/* fallthrough */;
 	case IOMAP_DISABLED:
 		return 0;
+	case IOMAP_FILEIO:
 	case IOMAP_ENABLED:
 		break;
 	}
@@ -1059,11 +1061,17 @@ static errcode_t confirm_iomap(struct fuse_conn_info *conn, struct fuse2fs *ff)
 
 static int iomap_enabled(const struct fuse2fs *ff)
 {
-	return ff->iomap_state == IOMAP_ENABLED;
+	return ff->iomap_state >= IOMAP_ENABLED;
+}
+
+static int iomap_does_fileio(const struct fuse2fs *ff)
+{
+	return ff->iomap_state == IOMAP_FILEIO;
 }
 #else
 # define confirm_iomap(...)	(0)
 # define iomap_enabled(...)	(0)
+# define iomap_does_fileio(...)	(0)
 #endif
 
 static void *op_init(struct fuse_conn_info *conn
@@ -1100,6 +1108,20 @@ static void *op_init(struct fuse_conn_info *conn
 	if (ff->iomap_state != IOMAP_DISABLED &&
 	    fuse_set_feature_flag(conn, FUSE_CAP_IOMAP))
 		ff->iomap_state = IOMAP_ENABLED;
+
+	/*
+	 * If iomap is turned on and the kernel advertises support for both
+	 * direct and pagecache IO, then that means the kernel handles all
+	 * regular file data block IO for us.  That means we can turn off all
+	 * of libext2fs' file data block handling except for inline data.
+	 *
+	 * XXX: kernel doesn't support inline data iomap
+	 */
+	if (iomap_enabled(ff) &&
+	    fuse_get_feature_flag(conn, FUSE_CAP_IOMAP_DIRECTIO) &&
+	    fuse_get_feature_flag(conn, FUSE_CAP_IOMAP_PAGECACHE))
+		ff->iomap_state = IOMAP_FILEIO;
+
 	/*
 	 * In iomap mode, the kernel writes file data directly to the block
 	 * device and does not flush the bdev page cache.  We must open the
@@ -4580,6 +4602,10 @@ static errcode_t clean_block_middle(struct fuse2fs *ff, ext2_ino_t ino,
 	int retflags;
 	errcode_t err;
 
+	/* the kernel does this for us in iomap mode */
+	if (iomap_does_fileio(ff))
+		return 0;
+
 	residue = FUSE2FS_OFF_IN_FSB(ff, offset);
 	if (residue == 0)
 		return 0;
@@ -4617,6 +4643,10 @@ static errcode_t clean_block_edge(struct fuse2fs *ff, ext2_ino_t ino,
 	off_t residue;
 	errcode_t err;
 
+	/* the kernel does this for us in iomap mode */
+	if (iomap_does_fileio(ff))
+		return 0;
+
 	residue = FUSE2FS_OFF_IN_FSB(ff, offset);
 	if (residue == 0)
 		return 0;