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kernel/include/linux/aio.h
Davide Libenzi 9c3060bedd signal/timer/event: KAIO eventfd support example 
This is an example about how to add eventfd support to the current KAIO code,
in order to enable KAIO to post readiness events to a pollable fd (hence
compatible with POSIX select/poll).  The KAIO code simply signals the eventfd
fd when events are ready, and this triggers a POLLIN in the fd.  This patch
uses a reserved for future use member of the struct iocb to pass an eventfd
file descriptor, that KAIO will use to post events every time a request
completes.  At that point, an aio_getevents() will return the completed result
to a struct io_event.  I made a quick test program to verify the patch, and it
runs fine here:

http://www.xmailserver.org/eventfd-aio-test.c

The test program uses poll(2), but it'd, of course, work with select and epoll
too.

This can allow to schedule both block I/O and other poll-able devices
requests, and wait for results using select/poll/epoll.  In a typical
scenario, an application would submit KAIO request using aio_submit(), and
will also use epoll_ctl() on the whole other class of devices (that with the
addition of signals, timers and user events, now it's pretty much complete),
and then would:

	epoll_wait(...);
	for_each_event {
		if (curr_event_is_kaiofd) {
			aio_getevents();
			dispatch_aio_events();
		} else {
			dispatch_epoll_event();
		}
	}

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-11 08:29:37 -07:00

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#ifndef __LINUX__AIO_H
#define __LINUX__AIO_H
#include <linux/list.h>
#include <linux/workqueue.h>
#include <linux/aio_abi.h>
#include <linux/uio.h>
#include <asm/atomic.h>
#include <linux/uio.h>
#define AIO_MAXSEGS 4
#define AIO_KIOGRP_NR_ATOMIC 8
struct kioctx;
/* Notes on cancelling a kiocb:
* If a kiocb is cancelled, aio_complete may return 0 to indicate
* that cancel has not yet disposed of the kiocb. All cancel
* operations *must* call aio_put_req to dispose of the kiocb
* to guard against races with the completion code.
*/
#define KIOCB_C_CANCELLED 0x01
#define KIOCB_C_COMPLETE 0x02
#define KIOCB_SYNC_KEY (~0U)
/* ki_flags bits */
/*
* 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
#define kiocbTryLock(iocb) test_and_set_bit(KIF_LOCKED, &(iocb)->ki_flags)
#define kiocbTryKick(iocb) test_and_set_bit(KIF_KICKED, &(iocb)->ki_flags)
#define kiocbSetLocked(iocb) set_bit(KIF_LOCKED, &(iocb)->ki_flags)
#define kiocbSetKicked(iocb) set_bit(KIF_KICKED, &(iocb)->ki_flags)
#define kiocbSetCancelled(iocb) set_bit(KIF_CANCELLED, &(iocb)->ki_flags)
#define kiocbClearLocked(iocb) clear_bit(KIF_LOCKED, &(iocb)->ki_flags)
#define kiocbClearKicked(iocb) clear_bit(KIF_KICKED, &(iocb)->ki_flags)
#define kiocbClearCancelled(iocb) clear_bit(KIF_CANCELLED, &(iocb)->ki_flags)
#define kiocbIsLocked(iocb) test_bit(KIF_LOCKED, &(iocb)->ki_flags)
#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;
int ki_users;
unsigned ki_key; /* id of this request */
struct file *ki_filp;
struct kioctx *ki_ctx; /* may be NULL for sync ops */
int (*ki_cancel)(struct kiocb *, struct io_event *);
ssize_t (*ki_retry)(struct kiocb *);
void (*ki_dtor)(struct kiocb *);
union {
void __user *user;
struct task_struct *tsk;
} ki_obj;
__u64 ki_user_data; /* user's data for completion */
wait_queue_t ki_wait;
loff_t ki_pos;
atomic_t ki_bio_count; /* num bio used for this iocb */
void *private;
/* State that we remember to be able to restart/retry */
unsigned short ki_opcode;
size_t ki_nbytes; /* copy of iocb->aio_nbytes */
char __user *ki_buf; /* remaining iocb->aio_buf */
size_t ki_left; /* remaining bytes */
struct iovec ki_inline_vec; /* inline vector */
struct iovec *ki_iovec;
unsigned long ki_nr_segs;
unsigned long ki_cur_seg;
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 file* to deliver event to.
*/
struct file *ki_eventfd;
};
#define is_sync_kiocb(iocb) ((iocb)->ki_key == KIOCB_SYNC_KEY)
#define init_sync_kiocb(x, filp) \
do { \
struct task_struct *tsk = current; \
(x)->ki_flags = 0; \
(x)->ki_users = 1; \
(x)->ki_key = KIOCB_SYNC_KEY; \
(x)->ki_filp = (filp); \
(x)->ki_ctx = NULL; \
(x)->ki_cancel = NULL; \
(x)->ki_retry = NULL; \
(x)->ki_dtor = NULL; \
(x)->ki_obj.tsk = tsk; \
(x)->ki_user_data = 0; \
init_wait((&(x)->ki_wait)); \
} while (0)
#define AIO_RING_MAGIC 0xa10a10a1
#define AIO_RING_COMPAT_FEATURES 1
#define AIO_RING_INCOMPAT_FEATURES 0
struct aio_ring {
unsigned id; /* kernel internal index number */
unsigned nr; /* number of io_events */
unsigned head;
unsigned tail;
unsigned magic;
unsigned compat_features;
unsigned incompat_features;
unsigned header_length; /* size of aio_ring */
struct io_event io_events[0];
}; /* 128 bytes + ring size */
#define aio_ring_avail(info, ring) (((ring)->head + (info)->nr - 1 - (ring)->tail) % (info)->nr)
#define AIO_RING_PAGES 8
struct aio_ring_info {
unsigned long mmap_base;
unsigned long mmap_size;
struct page **ring_pages;
spinlock_t ring_lock;
long nr_pages;
unsigned nr, tail;
struct page *internal_pages[AIO_RING_PAGES];
};
struct kioctx {
atomic_t users;
int dead;
struct mm_struct *mm;
/* This needs improving */
unsigned long user_id;
struct kioctx *next;
wait_queue_head_t wait;
spinlock_t ctx_lock;
int reqs_active;
struct list_head active_reqs; /* used for cancellation */
struct list_head run_list; /* used for kicked reqs */
/* sys_io_setup currently limits this to an unsigned int */
unsigned max_reqs;
struct aio_ring_info ring_info;
struct delayed_work wq;
};
/* prototypes */
extern unsigned aio_max_size;
extern ssize_t FASTCALL(wait_on_sync_kiocb(struct kiocb *iocb));
extern int FASTCALL(aio_put_req(struct kiocb *iocb));
extern void FASTCALL(kick_iocb(struct kiocb *iocb));
extern int FASTCALL(aio_complete(struct kiocb *iocb, long res, long res2));
extern void FASTCALL(__put_ioctx(struct kioctx *ctx));
struct mm_struct;
extern void FASTCALL(exit_aio(struct mm_struct *mm));
extern struct kioctx *lookup_ioctx(unsigned long ctx_id);
extern int FASTCALL(io_submit_one(struct kioctx *ctx,
struct iocb __user *user_iocb, struct iocb *iocb));
/* semi private, but used by the 32bit emulations: */
struct kioctx *lookup_ioctx(unsigned long ctx_id);
int FASTCALL(io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
struct iocb *iocb));
#define get_ioctx(kioctx) do { \
BUG_ON(atomic_read(&(kioctx)->users) <= 0); \
atomic_inc(&(kioctx)->users); \
} while (0)
#define put_ioctx(kioctx) do { \
BUG_ON(atomic_read(&(kioctx)->users) <= 0); \
if (unlikely(atomic_dec_and_test(&(kioctx)->users))) \
__put_ioctx(kioctx); \
} while (0)
#define in_aio() (unlikely(!is_sync_wait(current->io_wait)))
/* may be used for debugging */
#define warn_if_async() \
do { \
if (in_aio()) { \
printk(KERN_ERR "%s(%s:%d) called in async context!\n", \
__FUNCTION__, __FILE__, __LINE__); \
dump_stack(); \
} \
} while (0)
#define io_wait_to_kiocb(wait) container_of(wait, struct kiocb, ki_wait)
#include <linux/aio_abi.h>
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;
#endif /* __LINUX__AIO_H */
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