[PATCH] fuse: fix async read for legacy filesystems
While asynchronous reads mean a performance improvement in most cases, if
the filesystem assumed that reads are synchronous, then async reads may
degrade performance (filesystem may receive reads out of order, which can
confuse it's own readahead logic).
With sshfs a 1.5 to 4 times slowdown can be measured.
There's also a need for userspace filesystems to know whether asynchronous
reads are supported by the kernel or not.
To achive these, negotiate in the INIT request whether async reads will be
used and the maximum readahead value. Update interface version to 7.6
If userspace uses a version earlier than 7.6, then disable async reads, and
set maximum readahead value to the maximum read size, as done in previous
versions.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/fuse.h b/include/linux/fuse.h
index 528959c..5425b60 100644
--- a/include/linux/fuse.h
+++ b/include/linux/fuse.h
@@ -14,7 +14,7 @@
#define FUSE_KERNEL_VERSION 7
/** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 5
+#define FUSE_KERNEL_MINOR_VERSION 6
/** The node ID of the root inode */
#define FUSE_ROOT_ID 1
@@ -58,6 +58,9 @@
__u32 spare[6];
};
+/**
+ * Bitmasks for fuse_setattr_in.valid
+ */
#define FATTR_MODE (1 << 0)
#define FATTR_UID (1 << 1)
#define FATTR_GID (1 << 2)
@@ -75,6 +78,11 @@
#define FOPEN_DIRECT_IO (1 << 0)
#define FOPEN_KEEP_CACHE (1 << 1)
+/**
+ * INIT request/reply flags
+ */
+#define FUSE_ASYNC_READ (1 << 0)
+
enum fuse_opcode {
FUSE_LOOKUP = 1,
FUSE_FORGET = 2, /* no reply */
@@ -247,12 +255,16 @@
struct fuse_init_in {
__u32 major;
__u32 minor;
+ __u32 max_readahead;
+ __u32 flags;
};
struct fuse_init_out {
__u32 major;
__u32 minor;
- __u32 unused[3];
+ __u32 max_readahead;
+ __u32 flags;
+ __u32 unused;
__u32 max_write;
};