Messages in this thread | | | Date | Wed, 07 Nov 2007 16:34:22 +0100 | From | "Hillier, Gernot" <> | Subject | current status of Async I/O (io_submit & friends) on pipes |
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Hi!
Is the content of http://lse.sourceforge.net/io/aio.html still correct regarding support of pipes? Is there any up-to-date & authoritative interface description of io_submit & friends available?
This page tells me I'd receive EINVAL or the like when using async I/O on a pipe; however what I actually see on e.g. 2.6.23.1 is no error return, but an indefinite blocking in the io_submit syscall when the pipe is empty.
Is this expected behaviour?
Please put me on CC for any answer.
Here's a short snippet showing the behaviour. (link it against libaio - yes, I checked that libaio does nothing else than wrapping the syscalls).
------ SNIP -----
#include <unistd.h> #include <stdio.h> #include <errno.h> #include <libaio.h> #include <stdlib.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h>
int main() { int filedes[2]; char buf; io_context_t *ctx; struct iocb * cb;
ctx=(io_context_t *)malloc(sizeof(io_context_t)); memset(ctx,0,sizeof(io_context_t)); cb=(struct iocb *)malloc(1*sizeof(struct iocb)); memset(cb,0,1*sizeof(struct iocb));
pipe(filedes);
cb[0].aio_lio_opcode=IO_CMD_PREAD; cb[0].aio_fildes=filedes[0]; cb[0].u.c.buf=&buf; cb[0].u.c.nbytes=1;
printf("before read\n"); /* program will block here */ printf("io_submit %i\n",io_submit(*ctx,1,&cb)); printf("read completed\n"); }
-- Gernot Hillier
Siemens AG, CT SE 2 Corporate Competence Center Embedded Linux
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