fs: split generic and aio kiocb

Most callers in the kernel want to perform synchronous file I/O, but
still have to bloat the stack with a full struct kiocb.  Split out
the parts needed in filesystem code from those in the aio code, and
only allocate those needed to pass down argument on the stack.  The
aio code embedds the generic iocb in the one it allocates and can
easily get back to it by using container_of.

Also add a ->ki_complete method to struct kiocb, this is used to call
into the aio code and thus removes the dependency on aio for filesystems
impementing asynchronous operations.  It will also allow other callers
to substitute their own completion callback.

We also add a new ->ki_flags field to work around the nasty layering
violation recently introduced in commit 5e33f6 ("usb: gadget: ffs: add
eventfd notification about ffs events").

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 6 insertions, 40 deletions

diff --git a/include/linux/aio.h b/include/linux/aio.h
index f8516430490d..5c40b61285ac 100644
--- a/include/linux/aio.h
+++ b/include/linux/aio.h
@@ -14,67 +14,38 @@ struct kiocb;
 
 #define KIOCB_KEY               0
 
-/*
- * We use ki_cancel == KIOCB_CANCELLED to indicate that a kiocb has been either
- * cancelled or completed (this makes a certain amount of sense because
- * successful cancellation - io_cancel() - does deliver the completion to
- * userspace).
- *
- * And since most things don't implement kiocb cancellation and we'd really like
- * kiocb completion to be lockless when possible, we use ki_cancel to
- * synchronize cancellation and completion - we only set it to KIOCB_CANCELLED
- * with xchg() or cmpxchg(), see batch_complete_aio() and kiocb_cancel().
- */
-#define KIOCB_CANCELLED         ((void *) (~0ULL))
-
 typedef int (kiocb_cancel_fn)(struct kiocb *);
 
+#define IOCB_EVENTFD            (1 << 0)
+
 struct kiocb {
         struct file             *ki_filp;
-        struct kioctx           *ki_ctx;        /* NULL for sync ops */
-        kiocb_cancel_fn         *ki_cancel;
-        void                    *private;
-
-        union {
-                void __user             *user;
-        } ki_obj;
-
-        __u64                   ki_user_data;   /* user's data for completion */
         loff_t                  ki_pos;
-
-        struct list_head        ki_list;        /* the aio core uses this
-                                                 * for cancellation */
-
-        /*
-         * If the aio_resfd field of the userspace iocb is not zero,
-         * this is the underlying eventfd context to deliver events to.
-         */
-        struct eventfd_ctx      *ki_eventfd;
+        void (*ki_complete)(struct kiocb *iocb, long ret, long ret2);
+        void                    *private;
+        int                     ki_flags;
 };
 
 static inline bool is_sync_kiocb(struct kiocb *kiocb)
 {
-        return kiocb->ki_ctx == NULL;
+        return kiocb->ki_complete == NULL;
 }
 
 static inline void init_sync_kiocb(struct kiocb *kiocb, struct file *filp)
 {
         *kiocb = (struct kiocb) {
-                        .ki_ctx = NULL,
                         .ki_filp = filp,
                 };
 }
 
 /* prototypes */
 #ifdef CONFIG_AIO
-extern void aio_complete(struct kiocb *iocb, long res, long res2);
 struct mm_struct;
 extern void exit_aio(struct mm_struct *mm);
 extern long do_io_submit(aio_context_t ctx_id, long nr,
                          struct iocb __user *__user *iocbpp, bool compat);
 void kiocb_set_cancel_fn(struct kiocb *req, kiocb_cancel_fn *cancel);
 #else
-static inline void aio_complete(struct kiocb *iocb, long res, long res2) { }
 struct mm_struct;
 static inline void exit_aio(struct mm_struct *mm) { }
 static inline long do_io_submit(aio_context_t ctx_id, long nr,
@@ -84,11 +55,6 @@ static inline void kiocb_set_cancel_fn(struct kiocb *req,
                                        kiocb_cancel_fn *cancel) { }
 #endif /* CONFIG_AIO */
 
-static inline struct kiocb *list_kiocb(struct list_head *h)
-{
-        return list_entry(h, struct kiocb, ki_list);
-}
-
 /* for sysctl: */
 extern unsigned long aio_nr;
 extern unsigned long aio_max_nr;