Commit 9c3060bedd84144653a2ad7bea32389f65598d40
Committed by
Linus Torvalds
1 parent
fdb902b122
Exists in
master
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20 other branches
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>
Showing 3 changed files with 49 additions and 3 deletions Side-by-side Diff
fs/aio.c
... | ... | @@ -30,6 +30,7 @@ |
30 | 30 | #include <linux/highmem.h> |
31 | 31 | #include <linux/workqueue.h> |
32 | 32 | #include <linux/security.h> |
33 | +#include <linux/eventfd.h> | |
33 | 34 | |
34 | 35 | #include <asm/kmap_types.h> |
35 | 36 | #include <asm/uaccess.h> |
... | ... | @@ -417,6 +418,7 @@ |
417 | 418 | req->private = NULL; |
418 | 419 | req->ki_iovec = NULL; |
419 | 420 | INIT_LIST_HEAD(&req->ki_run_list); |
421 | + req->ki_eventfd = ERR_PTR(-EINVAL); | |
420 | 422 | |
421 | 423 | /* Check if the completion queue has enough free space to |
422 | 424 | * accept an event from this io. |
... | ... | @@ -458,6 +460,8 @@ |
458 | 460 | { |
459 | 461 | assert_spin_locked(&ctx->ctx_lock); |
460 | 462 | |
463 | + if (!IS_ERR(req->ki_eventfd)) | |
464 | + fput(req->ki_eventfd); | |
461 | 465 | if (req->ki_dtor) |
462 | 466 | req->ki_dtor(req); |
463 | 467 | if (req->ki_iovec != &req->ki_inline_vec) |
... | ... | @@ -942,6 +946,14 @@ |
942 | 946 | return 1; |
943 | 947 | } |
944 | 948 | |
949 | + /* | |
950 | + * Check if the user asked us to deliver the result through an | |
951 | + * eventfd. The eventfd_signal() function is safe to be called | |
952 | + * from IRQ context. | |
953 | + */ | |
954 | + if (!IS_ERR(iocb->ki_eventfd)) | |
955 | + eventfd_signal(iocb->ki_eventfd, 1); | |
956 | + | |
945 | 957 | info = &ctx->ring_info; |
946 | 958 | |
947 | 959 | /* add a completion event to the ring buffer. |
... | ... | @@ -1526,8 +1538,7 @@ |
1526 | 1538 | ssize_t ret; |
1527 | 1539 | |
1528 | 1540 | /* enforce forwards compatibility on users */ |
1529 | - if (unlikely(iocb->aio_reserved1 || iocb->aio_reserved2 || | |
1530 | - iocb->aio_reserved3)) { | |
1541 | + if (unlikely(iocb->aio_reserved1 || iocb->aio_reserved2)) { | |
1531 | 1542 | pr_debug("EINVAL: io_submit: reserve field set\n"); |
1532 | 1543 | return -EINVAL; |
1533 | 1544 | } |
... | ... | @@ -1550,6 +1561,19 @@ |
1550 | 1561 | if (unlikely(!req)) { |
1551 | 1562 | fput(file); |
1552 | 1563 | return -EAGAIN; |
1564 | + } | |
1565 | + if (iocb->aio_flags & IOCB_FLAG_RESFD) { | |
1566 | + /* | |
1567 | + * If the IOCB_FLAG_RESFD flag of aio_flags is set, get an | |
1568 | + * instance of the file* now. The file descriptor must be | |
1569 | + * an eventfd() fd, and will be signaled for each completed | |
1570 | + * event using the eventfd_signal() function. | |
1571 | + */ | |
1572 | + req->ki_eventfd = eventfd_fget((int) iocb->aio_resfd); | |
1573 | + if (unlikely(IS_ERR(req->ki_eventfd))) { | |
1574 | + ret = PTR_ERR(req->ki_eventfd); | |
1575 | + goto out_put_req; | |
1576 | + } | |
1553 | 1577 | } |
1554 | 1578 | |
1555 | 1579 | req->ki_filp = file; |
include/linux/aio.h
... | ... | @@ -119,6 +119,12 @@ |
119 | 119 | |
120 | 120 | struct list_head ki_list; /* the aio core uses this |
121 | 121 | * for cancellation */ |
122 | + | |
123 | + /* | |
124 | + * If the aio_resfd field of the userspace iocb is not zero, | |
125 | + * this is the underlying file* to deliver event to. | |
126 | + */ | |
127 | + struct file *ki_eventfd; | |
122 | 128 | }; |
123 | 129 | |
124 | 130 | #define is_sync_kiocb(iocb) ((iocb)->ki_key == KIOCB_SYNC_KEY) |
include/linux/aio_abi.h
... | ... | @@ -45,6 +45,14 @@ |
45 | 45 | IOCB_CMD_PWRITEV = 8, |
46 | 46 | }; |
47 | 47 | |
48 | +/* | |
49 | + * Valid flags for the "aio_flags" member of the "struct iocb". | |
50 | + * | |
51 | + * IOCB_FLAG_RESFD - Set if the "aio_resfd" member of the "struct iocb" | |
52 | + * is valid. | |
53 | + */ | |
54 | +#define IOCB_FLAG_RESFD (1 << 0) | |
55 | + | |
48 | 56 | /* read() from /dev/aio returns these structures. */ |
49 | 57 | struct io_event { |
50 | 58 | __u64 data; /* the data field from the iocb */ |
... | ... | @@ -84,7 +92,15 @@ |
84 | 92 | |
85 | 93 | /* extra parameters */ |
86 | 94 | __u64 aio_reserved2; /* TODO: use this for a (struct sigevent *) */ |
87 | - __u64 aio_reserved3; | |
95 | + | |
96 | + /* flags for the "struct iocb" */ | |
97 | + __u32 aio_flags; | |
98 | + | |
99 | + /* | |
100 | + * if the IOCB_FLAG_RESFD flag of "aio_flags" is set, this is an | |
101 | + * eventfd to signal AIO readiness to | |
102 | + */ | |
103 | + __u32 aio_resfd; | |
88 | 104 | }; /* 64 bytes */ |
89 | 105 | |
90 | 106 | #undef IFBIG |