diff options
Diffstat (limited to 'include/linux/aio.h')
| -rw-r--r-- | include/linux/aio.h | 41 |
1 files changed, 40 insertions, 1 deletions
diff --git a/include/linux/aio.h b/include/linux/aio.h index a4d5af907f9..0decf66117c 100644 --- a/include/linux/aio.h +++ b/include/linux/aio.h @@ -24,7 +24,12 @@ struct kioctx; #define KIOCB_SYNC_KEY (~0U) /* ki_flags bits */ -#define KIF_LOCKED 0 +/* + * This may be used for cancel/retry serialization in the future, but + * for now it's unused and we probably don't want modules to even + * think they can use it. + */ +/* #define KIF_LOCKED 0 */ #define KIF_KICKED 1 #define KIF_CANCELLED 2 @@ -43,6 +48,40 @@ struct kioctx; #define kiocbIsKicked(iocb) test_bit(KIF_KICKED, &(iocb)->ki_flags) #define kiocbIsCancelled(iocb) test_bit(KIF_CANCELLED, &(iocb)->ki_flags) +/* is there a better place to document function pointer methods? */ +/** + * ki_retry - iocb forward progress callback + * @kiocb: The kiocb struct to advance by performing an operation. + * + * This callback is called when the AIO core wants a given AIO operation + * to make forward progress. The kiocb argument describes the operation + * that is to be performed. As the operation proceeds, perhaps partially, + * ki_retry is expected to update the kiocb with progress made. Typically + * ki_retry is set in the AIO core and it itself calls file_operations + * helpers. + * + * ki_retry's return value determines when the AIO operation is completed + * and an event is generated in the AIO event ring. Except the special + * return values described below, the value that is returned from ki_retry + * is transferred directly into the completion ring as the operation's + * resulting status. Once this has happened ki_retry *MUST NOT* reference + * the kiocb pointer again. + * + * If ki_retry returns -EIOCBQUEUED it has made a promise that aio_complete() + * will be called on the kiocb pointer in the future. The AIO core will + * not ask the method again -- ki_retry must ensure forward progress. + * aio_complete() must be called once and only once in the future, multiple + * calls may result in undefined behaviour. + * + * If ki_retry returns -EIOCBRETRY it has made a promise that kick_iocb() + * will be called on the kiocb pointer in the future. This may happen + * through generic helpers that associate kiocb->ki_wait with a wait + * queue head that ki_retry uses via current->io_wait. It can also happen + * with custom tracking and manual calls to kick_iocb(), though that is + * discouraged. In either case, kick_iocb() must be called once and only + * once. ki_retry must ensure forward progress, the AIO core will wait + * indefinitely for kick_iocb() to be called. + */ struct kiocb { struct list_head ki_run_list; long ki_flags; |