[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 *.

drivers/block/loop.c

@@ -293,7 +293,7 @@ lo_read_actor(read_descriptor_t *desc, struct page *page,
 	      unsigned long offset, unsigned long size)
 {
 	unsigned long count = desc->count;
-	struct lo_read_data *p = (struct lo_read_data*)desc->buf;
+	struct lo_read_data *p = desc->arg.data;
 	struct loop_device *lo = p->lo;
 	sector_t IV;
 

fs/nfs/file.c

@@ -38,7 +38,7 @@ static long nfs_file_fcntl(int fd, unsigned int cmd,
 static int nfs_file_open(struct inode *, struct file *);
 static int nfs_file_release(struct inode *, struct file *);
 static int  nfs_file_mmap(struct file *, struct vm_area_struct *);
-static ssize_t nfs_file_sendfile(struct file *, loff_t *, size_t, read_actor_t, void __user *);
+static ssize_t nfs_file_sendfile(struct file *, loff_t *, size_t, read_actor_t, void *);
 static ssize_t nfs_file_read(struct kiocb *, char __user *, size_t, loff_t);
 static ssize_t nfs_file_write(struct kiocb *, const char __user *, size_t, loff_t);
 static int  nfs_file_flush(struct file *);
@@ -171,7 +171,7 @@ nfs_file_read(struct kiocb *iocb, char __user * buf, size_t count, loff_t pos)
 
 static ssize_t
 nfs_file_sendfile(struct file *filp, loff_t *ppos, size_t count,
-		read_actor_t actor, void __user *target)
+		read_actor_t actor, void *target)
 {
 	struct dentry *dentry = filp->f_dentry;
 	struct inode *inode = dentry->d_inode;

fs/nfsd/vfs.c

@@ -611,7 +611,7 @@ static int
 nfsd_read_actor(read_descriptor_t *desc, struct page *page, unsigned long offset , unsigned long size)
 {
 	unsigned long count = desc->count;
-	struct svc_rqst *rqstp = (struct svc_rqst *)desc->buf;
+	struct svc_rqst *rqstp = desc->arg.data;
 
 	if (size > count)
 		size = count;

fs/smbfs/file.c

@@ -261,7 +261,7 @@ smb_file_mmap(struct file * file, struct vm_area_struct * vma)
 
 static ssize_t
 smb_file_sendfile(struct file *file, loff_t *ppos,
-		  size_t count, read_actor_t actor, void __user *target)
+		  size_t count, read_actor_t actor, void *target)
 {
 	struct dentry *dentry = file->f_dentry;
 	ssize_t status;

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);

mm/filemap.c

@@ -836,9 +836,9 @@ int file_read_actor(read_descriptor_t *desc, struct page *page,
 	 * Faults on the destination of a read are common, so do it before
 	 * taking the kmap.
 	 */
-	if (!fault_in_pages_writeable(desc->buf, size)) {
+	if (!fault_in_pages_writeable(desc->arg.buf, size)) {
 		kaddr = kmap_atomic(page, KM_USER0);
-		left = __copy_to_user(desc->buf, kaddr + offset, size);
+		left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
 		kunmap_atomic(kaddr, KM_USER0);
 		if (left == 0)
 			goto success;
@@ -846,7 +846,7 @@ int file_read_actor(read_descriptor_t *desc, struct page *page,
 
 	/* Do it the slow way */
 	kaddr = kmap(page);
-	left = __copy_to_user(desc->buf, kaddr + offset, size);
+	left = __copy_to_user(desc->arg.buf, kaddr + offset, size);
 	kunmap(page);
 
 	if (left) {
@@ -856,7 +856,7 @@ int file_read_actor(read_descriptor_t *desc, struct page *page,
 success:
 	desc->count = count - size;
 	desc->written += size;
-	desc->buf += size;
+	desc->arg.buf += size;
 	return size;
 }
 
@@ -923,7 +923,7 @@ __generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 			read_descriptor_t desc;
 
 			desc.written = 0;
-			desc.buf = iov[seg].iov_base;
+			desc.arg.buf = iov[seg].iov_base;
 			desc.count = iov[seg].iov_len;
 			if (desc.count == 0)
 				continue;
@@ -973,7 +973,7 @@ int file_send_actor(read_descriptor_t * desc, struct page *page, unsigned long o
 {
 	ssize_t written;
 	unsigned long count = desc->count;
-	struct file *file = (struct file *) desc->buf;
+	struct file *file = desc->arg.data;
 
 	if (size > count)
 		size = count;
@@ -990,7 +990,7 @@ int file_send_actor(read_descriptor_t * desc, struct page *page, unsigned long o
 }
 
 ssize_t generic_file_sendfile(struct file *in_file, loff_t *ppos,
-			 size_t count, read_actor_t actor, void __user *target)
+			 size_t count, read_actor_t actor, void *target)
 {
 	read_descriptor_t desc;
 
@@ -999,7 +999,7 @@ ssize_t generic_file_sendfile(struct file *in_file, loff_t *ppos,
 
 	desc.written = 0;
 	desc.count = count;
-	desc.buf = target;
+	desc.arg.data = target;
 	desc.error = 0;
 
 	do_generic_file_read(in_file, ppos, &desc, actor);

mm/shmem.c

@@ -1474,7 +1474,7 @@ static ssize_t shmem_file_read(struct file *filp, char __user *buf, size_t count
 
 	desc.written = 0;
 	desc.count = count;
-	desc.buf = buf;
+	desc.arg.buf = buf;
 	desc.error = 0;
 
 	do_shmem_file_read(filp, ppos, &desc, file_read_actor);
@@ -1484,7 +1484,7 @@ static ssize_t shmem_file_read(struct file *filp, char __user *buf, size_t count
 }
 
 static ssize_t shmem_file_sendfile(struct file *in_file, loff_t *ppos,
-			 size_t count, read_actor_t actor, void __user *target)
+			 size_t count, read_actor_t actor, void *target)
 {
 	read_descriptor_t desc;
 
@@ -1493,7 +1493,7 @@ static ssize_t shmem_file_sendfile(struct file *in_file, loff_t *ppos,
 
 	desc.written = 0;
 	desc.count = count;
-	desc.buf = target;
+	desc.arg.data = target;
 	desc.error = 0;
 
 	do_shmem_file_read(in_file, ppos, &desc, actor);

net/sunrpc/xprt.c

@@ -973,7 +973,7 @@ static int
 tcp_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb,
 		unsigned int offset, size_t len)
 {
-	struct rpc_xprt *xprt = (struct rpc_xprt *)rd_desc->buf;
+	struct rpc_xprt *xprt = rd_desc->arg.data;
 	skb_reader_t desc = {
 		.skb	= skb,
 		.offset	= offset,
@@ -1021,7 +1021,7 @@ static void tcp_data_ready(struct sock *sk, int bytes)
 		goto out;
 
 	/* We use rd_desc to pass struct xprt to tcp_data_recv */
-	rd_desc.buf = (char *)xprt;
+	rd_desc.arg.data = xprt;
 	rd_desc.count = 65536;
 	tcp_read_sock(sk, &rd_desc, tcp_data_recv);
 out: