fs: clear or set FMODE_LSEEK based on llseek function

Pipe-like behaviour on llseek(2) (i.e. unconditionally failing with
-ESPIPE) can be expresses in 3 ways:
	1) ->llseek set to NULL in file_operations
	2) ->llseek set to no_llseek in file_operations
	3) FMODE_LSEEK *not* set in ->f_mode.

Enforce (3) in cases (1) and (2); that will allow to simplify the
checks and eventually get rid of no_llseek boilerplate.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/file_table.c b/fs/file_table.c
index 5424e3a..0658b82 100644 (file)
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -235,6 +235,8 @@ 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)
+               file->f_mode |= FMODE_LSEEK;
        if ((file->f_mode & FMODE_READ) &&
             likely(fop->read || fop->read_iter))
                file->f_mode |= FMODE_CAN_READ;

diff --git a/fs/open.c b/fs/open.c
index 1d57fbd..4488bd7 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -858,6 +858,10 @@ 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_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;