[PATCH v2 3/8] fs: clear or set FMODE_LSEEK based on llseek function

["Jason A. Donenfeld" <Jason@zx2c4.com>]

This helps unify a longstanding wart where FMODE_LSEEK hasn't been
uniformly unset when it should be.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 fs/file_table.c | 2 ++
 fs/open.c       | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/fs/file_table.c b/fs/file_table.c
index 5424e3a8df5f..933686f84bf8 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -243,6 +243,8 @@ static struct file *alloc_file(const struct path *path, int flags,
 		file->f_mode |= FMODE_CAN_WRITE;
 	file->f_mode |= FMODE_OPENED;
 	file->f_op = fop;
+	if (file->f_op->llseek)
+		file->f_mode |= FMODE_LSEEK;
 	if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 		i_readcount_inc(path->dentry->d_inode);
 	return file;
diff --git a/fs/open.c b/fs/open.c
index 1d57fbde2feb..07c332753a36 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -858,6 +858,8 @@ static int do_dentry_open(struct file *f,
 	if ((f->f_mode & FMODE_WRITE) &&
 	     likely(f->f_op->write || f->f_op->write_iter))
 		f->f_mode |= FMODE_CAN_WRITE;
+	if ((f->f_mode & FMODE_LSEEK) && !f->f_op->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;
 
-- 
2.35.1