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 <viro@zeniv.linux.org.uk>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/open.c b/fs/open.c
index 9d64679cec73..39d3d0468ee6 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -725,6 +725,10 @@ static int do_dentry_open(struct file *f,
         }
         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);