CODEWITHSUNDEEP
linux
Ming Ding
Ming Ding

Reputation: 129

What's the meaning of io_event.res2 parameter in asynchronous file IO?

I am using asynchronous IO api in my project, i am confused of the parameters io_event.res and io_event.res2

it seams that res means the io size, but what's the meaning of res2. Comments that i found in the file /usr/include/linux/aio.abi.h help nothing.

I will appriciate it so much if anyone explain that and shwo us an example.

/* read() from /dev/aio returns these structures. */
struct io_event {
        __u64           data;           /* the data field from the iocb */
        __u64           obj;            /* what iocb this event came from */
        __s64           res;            /* result code for this event */
        __s64           res2;           /* secondary result */
};

my code as below

size_t nevents = 2;
struct io_event events[nevents];
ret = io_getevents(ioctx, 1, nevents, events, NULL);
if (ret < 0) {
    perror("io_getevents");
    exit(1);
}

for (size_t i=0; i<ret; i++) {
    struct io_event *ev = &events[i];
    printf("Event returned with res=%lld res2=%lld\n", ev->res, ev->res2);
    nevents--;
}

Upvotes: 0

Views: 995

Answers (1)

jun.zhang
jun.zhang

Reputation: 11

res return the size of succeed io operation. if failed,res return the negative errno

Upvotes: 1

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