proc: mandate ->proc_lseek in "struct proc_ops"

Now that proc_ops are separate from file_operations and other operations
it easy to check all instances to have ->proc_lseek hook and remove check
in main code.

Note:
nonseekable_open() files naturally don't require ->proc_lseek.

Garbage collect pde_lseek() function.

[adobriyan@gmail.com: smoke test lseek()]
  Link: https://lkml.kernel.org/r/YG4OIhChOrVTPgdN@localhost.localdomain

Link: https://lkml.kernel.org/r/YFYX0Bzwxlc7aBa/@localhost.localdomain
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/isdn/capi/kcapi_proc.c

@@ -201,6 +201,7 @@ static ssize_t empty_read(struct file *file, char __user *buf,
 
 static const struct proc_ops empty_proc_ops = {
 	.proc_read	= empty_read,
+	.proc_lseek	= default_llseek,
 };
 
 // ---------------------------------------------------------------------------

drivers/net/wireless/intersil/hostap/hostap_proc.c

@@ -227,6 +227,7 @@ static ssize_t prism2_aux_dump_proc_no_read(struct file *file, char __user *buf,
 
 static const struct proc_ops prism2_aux_dump_proc_ops = {
 	.proc_read	= prism2_aux_dump_proc_no_read,
+	.proc_lseek	= default_llseek,
 };
 
 

drivers/scsi/esas2r/esas2r_main.c

@@ -616,6 +616,7 @@ static const struct file_operations esas2r_proc_fops = {
 };
 
 static const struct proc_ops esas2r_proc_ops = {
+	.proc_lseek		= default_llseek,
 	.proc_ioctl		= esas2r_proc_ioctl,
 #ifdef CONFIG_COMPAT
 	.proc_compat_ioctl	= compat_ptr_ioctl,

fs/proc/inode.c

@@ -273,25 +273,15 @@ void proc_entry_rundown(struct proc_dir_entry *de)
 	spin_unlock(&de->pde_unload_lock);
 }
 
-static loff_t pde_lseek(struct proc_dir_entry *pde, struct file *file, loff_t offset, int whence)
-{
-	typeof_member(struct proc_ops, proc_lseek) lseek;
-
-	lseek = pde->proc_ops->proc_lseek;
-	if (!lseek)
-		lseek = default_llseek;
-	return lseek(file, offset, whence);
-}
-
 static loff_t proc_reg_llseek(struct file *file, loff_t offset, int whence)
 {
 	struct proc_dir_entry *pde = PDE(file_inode(file));
 	loff_t rv = -EINVAL;
 
 	if (pde_is_permanent(pde)) {
-		return pde_lseek(pde, file, offset, whence);
+		return pde->proc_ops->proc_lseek(file, offset, whence);
 	} else if (use_pde(pde)) {
-		rv = pde_lseek(pde, file, offset, whence);
+		rv = pde->proc_ops->proc_lseek(file, offset, whence);
 		unuse_pde(pde);
 	}
 	return rv;

include/linux/proc_fs.h

@@ -32,6 +32,7 @@ struct proc_ops {
 	ssize_t	(*proc_read)(struct file *, char __user *, size_t, loff_t *);
 	ssize_t (*proc_read_iter)(struct kiocb *, struct iov_iter *);
 	ssize_t	(*proc_write)(struct file *, const char __user *, size_t, loff_t *);
+	/* mandatory unless nonseekable_open() or equivalent is used */
 	loff_t	(*proc_lseek)(struct file *, loff_t, int);
 	int	(*proc_release)(struct inode *, struct file *);
 	__poll_t (*proc_poll)(struct file *, struct poll_table_struct *);

tools/testing/selftests/proc/read.c

@@ -14,7 +14,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 // Test
-// 1) read of every file in /proc
+// 1) read and lseek on every file in /proc
 // 2) readlink of every symlink in /proc
 // 3) recursively (1) + (2) for every directory in /proc
 // 4) write to /proc/*/clear_refs and /proc/*/task/*/clear_refs
@@ -45,6 +45,8 @@ static void f_reg(DIR *d, const char *filename)
 	fd = openat(dirfd(d), filename, O_RDONLY|O_NONBLOCK);
 	if (fd == -1)
 		return;
+	/* struct proc_ops::proc_lseek is mandatory if file is seekable. */
+	(void)lseek(fd, 0, SEEK_SET);
 	rv = read(fd, buf, sizeof(buf));
 	assert((0 <= rv && rv <= sizeof(buf)) || rv == -1);
 	close(fd);