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Date:   Wed, 13 Jan 2021 16:27:21 -0800
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Subject: [RFC PATCH v1 3/5] libext2fs: allow the unix_io manager's cache to be
 disabled and re-enabled
From:   Saranya Muruganandam <saranyamohan@google.com>
To:     linux-ext4@vger.kernel.org
Cc:     tytso@mit.edu
Content-Type: text/plain; charset="UTF-8"
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From: Theodore Ts'o <tytso@mit.edu>

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 lib/ext2fs/ext2_io.h |  1 +
 lib/ext2fs/unix_io.c | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/lib/ext2fs/ext2_io.h b/lib/ext2fs/ext2_io.h
index 2e0da5a5..95c25a7b 100644
--- a/lib/ext2fs/ext2_io.h
+++ b/lib/ext2fs/ext2_io.h
@@ -106,6 +106,7 @@ struct struct_io_manager {
 #define IO_FLAG_DIRECT_IO	0x0004
 #define IO_FLAG_FORCE_BOUNCE	0x0008
 #define IO_FLAG_THREADS		0x0010
+#define IO_FLAG_NOCACHE		0x0020
 
 /*
  * Convenience functions....
diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index 9385487d..2df53e51 100644
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -942,6 +942,8 @@ static errcode_t unix_read_blk64(io_channel channel, unsigned long long block,
 #ifdef NO_IO_CACHE
 	return raw_read_blk(channel, data, block, count, buf);
 #else
+	if (data->flags & IO_FLAG_NOCACHE)
+		return raw_read_blk(channel, data, block, count, buf);
 	/*
 	 * If we're doing an odd-sized read or a very large read,
 	 * flush out the cache and then do a direct read.
@@ -1032,6 +1034,8 @@ static errcode_t unix_write_blk64(io_channel channel, unsigned long long block,
 #ifdef NO_IO_CACHE
 	return raw_write_blk(channel, data, block, count, buf);
 #else
+	if (data->flags & IO_FLAG_NOCACHE)
+		return raw_write_blk(channel, data, block, count, buf);
 	/*
 	 * If we're doing an odd-sized write or a very large write,
 	 * flush out the cache completely and then do a direct write.
@@ -1161,6 +1165,7 @@ static errcode_t unix_set_option(io_channel channel, const char *option,
 {
 	struct unix_private_data *data;
 	unsigned long long tmp;
+	errcode_t retval;
 	char *end;
 
 	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
@@ -1179,6 +1184,20 @@ static errcode_t unix_set_option(io_channel channel, const char *option,
 			return EXT2_ET_INVALID_ARGUMENT;
 		return 0;
 	}
+	if (!strcmp(option, "cache")) {
+		if (!arg)
+			return EXT2_ET_INVALID_ARGUMENT;
+		if (!strcmp(arg, "on")) {
+			data->flags &= ~IO_FLAG_NOCACHE;
+			return 0;
+		}
+		if (!strcmp(arg, "off")) {
+			retval = flush_cached_blocks(channel, data, 0);
+			data->flags |= IO_FLAG_NOCACHE;
+			return retval;
+		}
+		return EXT2_ET_INVALID_ARGUMENT;
+	}
 	return EXT2_ET_INVALID_ARGUMENT;
 }
 
-- 
2.30.0.284.gd98b1dd5eaa7-goog