linux-ext4 - [PATCH 09/10] libext2fs: allow callers to disallow I/O to file data blocks

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Message-ID: <175573713497.21546.14774021956944380330.stgit@frogsfrogsfrogs>
Date: Wed, 20 Aug 2025 18:15:25 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: John@...ves.net, bernd@...ernd.com, linux-fsdevel@...r.kernel.org,
 linux-ext4@...r.kernel.org, miklos@...redi.hu, joannelkoong@...il.com,
 neal@...pa.dev
Subject: [PATCH 09/10] libext2fs: allow callers to disallow I/O to file data
 blocks

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

Add a flag to ext2_file_t to disallow read and write I/O to file data
blocks.  This supports fuse2fs iomap support, which will keep all the
file data I/O inside the kerne.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 lib/ext2fs/ext2fs.h |    3 +++
 lib/ext2fs/fileio.c |   12 +++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)


diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index dee9feb02624ed..7d36b1a839dc57 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -178,6 +178,9 @@ typedef struct ext2_struct_dblist *ext2_dblist;
 #define EXT2_FILE_WRITE		0x0001
 #define EXT2_FILE_CREATE	0x0002
 
+/* no file I/O to disk blocks, only to inline data */
+#define EXT2_FILE_NOBLOCKIO	0x0004
+
 #define EXT2_FILE_MASK		0x00FF
 
 #define EXT2_FILE_BUF_DIRTY	0x4000
diff --git a/lib/ext2fs/fileio.c b/lib/ext2fs/fileio.c
index 3a36e9e7fff43b..95ee45ec7371ae 100644
--- a/lib/ext2fs/fileio.c
+++ b/lib/ext2fs/fileio.c
@@ -314,6 +314,11 @@ errcode_t ext2fs_file_read(ext2_file_t file, void *buf,
 	if (file->inode.i_flags & EXT4_INLINE_DATA_FL)
 		return ext2fs_file_read_inline_data(file, buf, wanted, got);
 
+	if (file->flags & EXT2_FILE_NOBLOCKIO) {
+		retval = EXT2_ET_OP_NOT_SUPPORTED;
+		goto fail;
+	}
+
 	while ((file->pos < EXT2_I_SIZE(&file->inode)) && (wanted > 0)) {
 		retval = sync_buffer_position(file);
 		if (retval)
@@ -441,6 +446,11 @@ errcode_t ext2fs_file_write(ext2_file_t file, const void *buf,
 		retval = 0;
 	}
 
+	if (file->flags & EXT2_FILE_NOBLOCKIO) {
+		retval = EXT2_ET_OP_NOT_SUPPORTED;
+		goto fail;
+	}
+
 	while (nbytes > 0) {
 		retval = sync_buffer_position(file);
 		if (retval)
@@ -609,7 +619,7 @@ static errcode_t ext2fs_file_zero_past_offset(ext2_file_t file,
 	int ret_flags;
 	errcode_t retval;
 
-	if (off == 0)
+	if (off == 0 || (file->flags & EXT2_FILE_NOBLOCKIO))
 		return 0;
 
 	retval = sync_buffer_position(file);