fs: remove no_llseek

Now that all callers of ->llseek are going through vfs_llseek(), we
don't gain anything by keeping no_llseek around. Nothing actually calls
it and setting ->llseek to no_lseek is completely equivalent to
leaving it NULL.

Longer term (== by the end of merge window) we want to remove all such
intializations.  To simplify the merge window this commit does *not*
touch initializers - it only defines no_llseek as NULL (and simplifies
the tests on file opening).

At -rc1 we'll need do a mechanical removal of no_llseek -

git grep -l -w no_llseek | grep -v porting.rst | while read i; do
	sed -i '/\<no_llseek\>/d' $i
done
would do it.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Documentation/filesystems/porting.rst

@@ -914,3 +914,11 @@ Calling conventions for file_open_root() changed; now it takes struct path *
 instead of passing mount and dentry separately.  For callers that used to
 pass <mnt, mnt->mnt_root> pair (i.e. the root of given mount), a new helper
 is provided - file_open_root_mnt().  In-tree users adjusted.
+
+---
+
+**mandatory**
+
+no_llseek is gone; don't set .llseek to that - just leave it NULL instead.
+Checks for "does that file have llseek(2), or should it fail with ESPIPE"
+should be done by looking at FMODE_LSEEK in file->f_mode.

drivers/gpu/drm/drm_file.c

@@ -552,8 +552,7 @@ EXPORT_SYMBOL(drm_release_noglobal);
  * Since events are used by the KMS API for vblank and page flip completion this
  * means all modern display drivers must use it.
  *
- * @offset is ignored, DRM events are read like a pipe. Therefore drivers also
- * must set the &file_operation.llseek to no_llseek(). Polling support is
+ * @offset is ignored, DRM events are read like a pipe. Polling support is
  * provided by drm_poll().
  *
  * This function will only ever read a full event. Therefore userspace must

fs/file_table.c

@@ -235,7 +235,7 @@ static struct file *alloc_file(const struct path *path, int flags,
 	file->f_mapping = path->dentry->d_inode->i_mapping;
 	file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
 	file->f_sb_err = file_sample_sb_err(file);
-	if (fop->llseek && fop->llseek != no_llseek)
+	if (fop->llseek)
 		file->f_mode |= FMODE_LSEEK;
 	if ((file->f_mode & FMODE_READ) &&
 	     likely(fop->read || fop->read_iter))

fs/open.c

@@ -860,8 +860,6 @@ static int do_dentry_open(struct file *f,
 		f->f_mode |= FMODE_CAN_WRITE;
 	if ((f->f_mode & FMODE_LSEEK) && !f->f_op->llseek)
 		f->f_mode &= ~FMODE_LSEEK;
-	if ((f->f_mode & FMODE_LSEEK) && f->f_op->llseek == no_llseek)
-		f->f_mode &= ~FMODE_LSEEK;
 	if (f->f_mapping->a_ops && f->f_mapping->a_ops->direct_IO)
 		f->f_mode |= FMODE_CAN_ODIRECT;
 

fs/read_write.c

@@ -227,12 +227,6 @@ loff_t noop_llseek(struct file *file, loff_t offset, int whence)
 }
 EXPORT_SYMBOL(noop_llseek);
 
-loff_t no_llseek(struct file *file, loff_t offset, int whence)
-{
-	return -ESPIPE;
-}
-EXPORT_SYMBOL(no_llseek);
-
 loff_t default_llseek(struct file *file, loff_t offset, int whence)
 {
 	struct inode *inode = file_inode(file);

include/linux/fs.h

@@ -3022,7 +3022,7 @@ extern long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
 extern void
 file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
 extern loff_t noop_llseek(struct file *file, loff_t offset, int whence);
-extern loff_t no_llseek(struct file *file, loff_t offset, int whence);
+#define no_llseek NULL
 extern loff_t vfs_setpos(struct file *file, loff_t offset, loff_t maxsize);
 extern loff_t generic_file_llseek(struct file *file, loff_t offset, int whence);
 extern loff_t generic_file_llseek_size(struct file *file, loff_t offset,

kernel/bpf/bpf_iter.c

@@ -81,10 +81,9 @@ static bool bpf_iter_support_resched(struct seq_file *seq)
 #define MAX_ITER_OBJECTS	1000000
 
 /* bpf_seq_read, a customized and simpler version for bpf iterator.
- * no_llseek is assumed for this file.
  * The following are differences from seq_read():
  *  . fixed buffer size (PAGE_SIZE)
- *  . assuming no_llseek
+ *  . assuming NULL ->llseek()
  *  . stop() may call bpf program, handling potential overflow there
  */
 static ssize_t bpf_seq_read(struct file *file, char __user *buf, size_t size,