[PATCH] sparse: read_descriptor_t annotation

We have a fun situation with read_descriptor_t - all its instances end
up passed to some actor; these actors use desc->buf as their private
data; there are 5 of them and they expect resp:

        struct lo_read_data *
        struct svc_rqst *
        struct file *
        struct rpc_xprt *
        char __user *

IOW, there is no type safety whatsoever; the field is essentially untyped,
we rely on the fact that actor is chosen by the same code that sets ->buf
and expect it to put something of the right type there.

Right now desc->buf is declared as char __user *.  Moreover, the last
argument of ->sendfile() (what should be stored in ->buf) is void __user *,
even though it's actually _never_ a userland pointer.

If nothing else, ->sendfile() should take void * instead; that alone removes
a bunch of bogus warnings.  I went further and replaced desc->buf with a
union of void * and char __user *.

1 files changed, 6 insertions, 3 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3d24beb4ac36..819e67e3a95b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -852,7 +852,10 @@ struct block_device_operations {
 typedef struct {
 	size_t written;
 	size_t count;
-	char __user * buf;
+	union {
+		char __user * buf;
+		void *data;
+	} arg;
 	int error;
 } read_descriptor_t;
 
@@ -883,7 +886,7 @@ struct file_operations {
 	int (*lock) (struct file *, int, struct file_lock *);
 	ssize_t (*readv) (struct file *, const struct iovec *, unsigned long, loff_t *);
 	ssize_t (*writev) (struct file *, const struct iovec *, unsigned long, loff_t *);
-	ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t, void __user *);
+	ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t, void *);
 	ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
 	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
 	long (*fcntl)(int fd, unsigned int cmd,
@@ -1410,7 +1413,7 @@ extern ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, lof
 extern ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos);
 ssize_t generic_file_write_nolock(struct file *file, const struct iovec *iov,
 				unsigned long nr_segs, loff_t *ppos);
-extern ssize_t generic_file_sendfile(struct file *, loff_t *, size_t, read_actor_t, void __user *);
+extern ssize_t generic_file_sendfile(struct file *, loff_t *, size_t, read_actor_t, void *);
 extern void do_generic_mapping_read(struct address_space *mapping,
 				    struct file_ra_state *, struct file *,
 				    loff_t *, read_descriptor_t *, read_actor_t);