replace checking for ->read/->aio_read presence with check in ->f_mode

Since we are about to introduce new methods (read_iter/write_iter), the
tests in a bunch of places would have to grow inconveniently. Check
once (at open() time) and store results in ->f_mode as FMODE_CAN_READ
and FMODE_CAN_WRITE resp. It might end up being a temporary measure -
once everything switches from ->aio_{read,write} to ->{read,write}_iter
it might make sense to return to open-coded checks. We'll see...

Signed-off-by: Al Viro <[e-mail]>

drivers/mtd/nand/nandsim.c

···
 		cfile = filp_open(cache_file, O_CREAT | O_RDWR | O_LARGEFILE, 0600);
 		if (IS_ERR(cfile))
 			return PTR_ERR(cfile);
-		if (!cfile->f_op->read && !cfile->f_op->aio_read) {
+		if (!(cfile->f_mode & FMODE_CAN_READ)) {
 			NS_ERR("alloc_device: cache file not readable\n");
 			err = -EINVAL;
 			goto err_close;
 		}
-		if (!cfile->f_op->write && !cfile->f_op->aio_write) {
+		if (!(cfile->f_mode & FMODE_CAN_WRITE)) {
 			NS_ERR("alloc_device: cache file not writeable\n");
 			err = -EINVAL;
 			goto err_close;

drivers/usb/gadget/storage_common.c

···
 	 * If we can't read the file, it's no good.
 	 * If we can't write the file, use it read-only.
 	 */
-	if (!(filp->f_op->read || filp->f_op->aio_read)) {
+	if (!(filp->f_mode & FMODE_CAN_READ)) {
 		LINFO(curlun, "file not readable: %s\n", filename);
 		goto out;
 	}
-	if (!(filp->f_op->write || filp->f_op->aio_write))
+	if (!(filp->f_mode & FMODE_CAN_WRITE))
 		ro = 1;
 
 	size = i_size_read(inode->i_mapping->host);

fs/file_table.c

···
 	file->f_path = *path;
 	file->f_inode = path->dentry->d_inode;
 	file->f_mapping = path->dentry->d_inode->i_mapping;
+	if ((mode & FMODE_READ) && likely(fop->read || fop->aio_read))
+		mode |= FMODE_CAN_READ;
+	if ((mode & FMODE_WRITE) && likely(fop->write || fop->aio_write))
+		mode |= FMODE_CAN_WRITE;
 	file->f_mode = mode;
 	file->f_op = fop;
 	if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)

fs/open.c

···
 	}
 	if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 		i_readcount_inc(inode);
+	if ((f->f_mode & FMODE_READ) && likely(f->f_op->read || f->f_op->aio_read))
+		f->f_mode |= FMODE_CAN_READ;
+	if ((f->f_mode & FMODE_WRITE) && likely(f->f_op->write || f->f_op->aio_write))
+		f->f_mode |= FMODE_CAN_WRITE;
 
 	f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 

fs/read_write.c

···
 
 	if (!(file->f_mode & FMODE_READ))
 		return -EBADF;
-	if (!file->f_op->read && !file->f_op->aio_read)
+	if (!(file->f_mode & FMODE_CAN_READ))
 		return -EINVAL;
 	if (unlikely(!access_ok(VERIFY_WRITE, buf, count)))
 		return -EFAULT;
···
 	const char __user *p;
 	ssize_t ret;
 
-	if (!file->f_op->write && !file->f_op->aio_write)
+	if (!(file->f_mode & FMODE_CAN_WRITE))
 		return -EINVAL;
 
 	old_fs = get_fs();
···
 
 	if (!(file->f_mode & FMODE_WRITE))
 		return -EBADF;
-	if (!file->f_op->write && !file->f_op->aio_write)
+	if (!(file->f_mode & FMODE_CAN_WRITE))
 		return -EINVAL;
 	if (unlikely(!access_ok(VERIFY_READ, buf, count)))
 		return -EFAULT;
···
 {
 	if (!(file->f_mode & FMODE_READ))
 		return -EBADF;
-	if (!file->f_op->aio_read && !file->f_op->read)
+	if (!(file->f_mode & FMODE_CAN_READ))
 		return -EINVAL;
 
 	return do_readv_writev(READ, file, vec, vlen, pos);
···
 {
 	if (!(file->f_mode & FMODE_WRITE))
 		return -EBADF;
-	if (!file->f_op->aio_write && !file->f_op->write)
+	if (!(file->f_mode & FMODE_CAN_WRITE))
 		return -EINVAL;
 
 	return do_readv_writev(WRITE, file, vec, vlen, pos);
···
 		goto out;
 
 	ret = -EINVAL;
-	if (!file->f_op->aio_read && !file->f_op->read)
+	if (!(file->f_mode & FMODE_CAN_READ))
 		goto out;
 
 	ret = compat_do_readv_writev(READ, file, vec, vlen, pos);
···
 		goto out;
 
 	ret = -EINVAL;
-	if (!file->f_op->aio_write && !file->f_op->write)
+	if (!(file->f_mode & FMODE_CAN_WRITE))
 		goto out;
 
 	ret = compat_do_readv_writev(WRITE, file, vec, vlen, pos);

include/linux/fs.h

···
 #define FMODE_ATOMIC_POS	((__force fmode_t)0x8000)
 /* Write access to underlying fs */
 #define FMODE_WRITER		((__force fmode_t)0x10000)
+/* Has read method(s) */
+#define FMODE_CAN_READ          ((__force fmode_t)0x20000)
+/* Has write method(s) */
+#define FMODE_CAN_WRITE         ((__force fmode_t)0x40000)
 
 /* File was opened by fanotify and shouldn't generate fanotify events */
 #define FMODE_NONOTIFY		((__force fmode_t)0x1000000)