fuse: add blksize field to fuse_attr

There are cases when the filesystem will be passed the buffer from a single
read or write call, namely:

 1) in 'direct-io' mode (not O_DIRECT), read/write requests don't go
    through the page cache, but go directly to the userspace fs

 2) currently buffered writes are done with single page requests, but
    if Nick's ->perform_write() patch goes it, it will be possible to
    do larger write requests.  But only if the original write() was
    also bigger than a page.

In these cases the filesystem might want to give a hint to the app
about the optimal I/O size.

Allow the userspace filesystem to supply a blksize value to be returned by
stat() and friends.  If the field is zero, it defaults to the old
PAGE_CACHE_SIZE value.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/fuse.h

@@ -15,6 +15,7 @@
  *  - new fuse_getattr_in input argument of GETATTR
  *  - add lk_flags in fuse_lk_in
  *  - add lock_owner field to fuse_setattr_in, fuse_read_in and fuse_write_in
+ *  - add blksize field to fuse_attr
  */
 
 #include <asm/types.h>
@@ -53,6 +54,8 @@ struct fuse_attr {
 	__u32	uid;
 	__u32	gid;
 	__u32	rdev;
+	__u32	blksize;
+	__u32	padding;
 };
 
 struct fuse_kstatfs {
@@ -177,6 +180,8 @@ enum fuse_opcode {
 /* The read buffer is required to be at least 8k, but may be much larger */
 #define FUSE_MIN_READ_BUFFER 8192
 
+#define FUSE_COMPAT_ENTRY_OUT_SIZE 120
+
 struct fuse_entry_out {
 	__u64	nodeid;		/* Inode ID */
 	__u64	generation;	/* Inode generation: nodeid:gen must
@@ -198,6 +203,8 @@ struct fuse_getattr_in {
 	__u64	fh;
 };
 
+#define FUSE_COMPAT_ATTR_OUT_SIZE 96
+
 struct fuse_attr_out {
 	__u64	attr_valid;	/* Cache timeout for the attributes */
 	__u32	attr_valid_nsec;