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authorIan Campbell <ian.campbell@citrix.com>2013-07-31 16:15:51 +0100
committerIan Campbell <ian.campbell@citrix.com>2013-08-20 15:34:03 +0100
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treee5ce4b22b9fc9f68036937aa931059aee6c79491 /tools/libaio/man/io.3
parent03145f0fe42c007834c1ef50d95fe6c4f58a326a (diff)
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tools: remove in tree libaio
We have defaulted to using the system libaio for a while now and I din't think there are any relevant distros which don't have it that running Xen 4.4 would be reasonable on. Also it has caused confusion because it is not ever wanted on ARM, but the build system doesn't express that (could be fixed, but deleting is the right thing to do anyway). Signed-off-by: Ian Campbell <ian.campbell@citrix.com> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com> Acked-by: Matt Wilson <msw@amazon.com> Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
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-.TH io 3 2002-09-12 "Linux 2.4" Linux IO"
-.SH NAME
-io \- Asynchronous IO
-.SH SYNOPSYS
-.nf
-.B #include <errno.h>
-.sp
-.br
-.B #include <libio.h>
-.sp
-.fi
-.SH DESCRIPTION
-The libaio library defines a new set of I/O operations which can
-significantly reduce the time an application spends waiting at I/O. The
-new functions allow a program to initiate one or more I/O operations and
-then immediately resume normal work while the I/O operations are
-executed in parallel.
-
-These functions are part of the library with realtime functions named
-.IR "libaio"
-. They are not actually part of the
-.IR "libc"
-binary.
-The implementation of these functions can be done using support in the
-kernel.
-
-All IO operations operate on files which were opened previously. There
-might be arbitrarily many operations running for one file. The
-asynchronous I/O operations are controlled using a data structure named
-.IR "struct iocb"
-It is defined in
-.IR "libio.h"
-as follows.
-
-.nf
-
-typedef struct io_context *io_context_t;
-
-typedef enum io_iocb_cmd {
- IO_CMD_PREAD = 0,
- IO_CMD_PWRITE = 1,
-
- IO_CMD_FSYNC = 2,
- IO_CMD_FDSYNC = 3,
-
- IO_CMD_POLL = 5,
- IO_CMD_NOOP = 6,
-} io_iocb_cmd_t;
-
-struct io_iocb_common {
- void *buf;
- unsigned __pad1;
- long nbytes;
- unsigned __pad2;
- long long offset;
- long long __pad3, __pad4;
-}; /* result code is the amount read or -'ve errno */
-
-
-struct iocb {
- void *data;
- unsigned key;
- short aio_lio_opcode;
- short aio_reqprio;
- int aio_fildes;
- union {
- struct io_iocb_common c;
- struct io_iocb_vector v;
- struct io_iocb_poll poll;
- struct io_iocb_sockaddr saddr;
- } u;
-};
-
-
-.fi
-.TP
-.IR "int aio_fildes"
-This element specifies the file descriptor to be used for the
-operation. It must be a legal descriptor, otherwise the operation will
-fail.
-
-The device on which the file is opened must allow the seek operation.
-I.e., it is not possible to use any of the IO operations on devices
-like terminals where an
-.IR "lseek"
-call would lead to an error.
-.TP
-.IR "long u.c.offset"
-This element specifies the offset in the file at which the operation (input
-or output) is performed. Since the operations are carried out in arbitrary
-order and more than one operation for one file descriptor can be
-started, one cannot expect a current read/write position of the file
-descriptor.
-.TP
-.IR "void *buf"
-This is a pointer to the buffer with the data to be written or the place
-where the read data is stored.
-.TP
-.IR "long u.c.nbytes"
-This element specifies the length of the buffer pointed to by
-.IR "io_buf"
-.
-.TP
-.IR "int aio_reqprio"
-Is not currently used.
-.TP
-.B "IO_CMD_PREAD"
-Start a read operation. Read from the file at position
-.IR "u.c.offset"
-and store the next
-.IR "u.c.nbytes"
-bytes in the
-buffer pointed to by
-.IR "buf"
-.
-.TP
-.B "IO_CMD_PWRITE"
-Start a write operation. Write
-.IR "u.c.nbytes"
-bytes starting at
-.IR "buf"
-into the file starting at position
-.IR "u.c.offset"
-.
-.TP
-.B "IO_CMD_NOP"
-Do nothing for this control block. This value is useful sometimes when
-an array of
-.IR "struct iocb"
-values contains holes, i.e., some of the
-values must not be handled although the whole array is presented to the
-.IR "io_submit"
-function.
-.TP
-.B "IO_CMD_FSYNC"
-.TP
-.B "IO_CMD_POLL"
-This is experimental.
-.SH EXAMPLE
-.nf
-/*
- * Simplistic version of copy command using async i/o
- *
- * From: Stephen Hemminger <shemminger@osdl.org>
- * Copy file by using a async I/O state machine.
- * 1. Start read request
- * 2. When read completes turn it into a write request
- * 3. When write completes decrement counter and free resources
- *
- *
- * Usage: aiocp file(s) desination
- */
-
-#include <unistd.h>
-#include <stdio.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/param.h>
-#include <fcntl.h>
-#include <errno.h>
-
-#include <libaio.h>
-
-#define AIO_BLKSIZE (64*1024)
-#define AIO_MAXIO 32
-
-static int busy = 0; // # of I/O's in flight
-static int tocopy = 0; // # of blocks left to copy
-static int dstfd = -1; // destination file descriptor
-static const char *dstname = NULL;
-static const char *srcname = NULL;
-
-
-/* Fatal error handler */
-static void io_error(const char *func, int rc)
-{
- if (rc == -ENOSYS)
- fprintf(stderr, "AIO not in this kernel\n");
- else if (rc < 0 && -rc < sys_nerr)
- fprintf(stderr, "%s: %s\n", func, sys_errlist[-rc]);
- else
- fprintf(stderr, "%s: error %d\n", func, rc);
-
- if (dstfd > 0)
- close(dstfd);
- if (dstname)
- unlink(dstname);
- exit(1);
-}
-
-/*
- * Write complete callback.
- * Adjust counts and free resources
- */
-static void wr_done(io_context_t ctx, struct iocb *iocb, long res, long res2)
-{
- if (res2 != 0) {
- io_error("aio write", res2);
- }
- if (res != iocb->u.c.nbytes) {
- fprintf(stderr, "write missed bytes expect %d got %d\n", iocb->u.c.nbytes, res2);
- exit(1);
- }
- --tocopy;
- --busy;
- free(iocb->u.c.buf);
-
- memset(iocb, 0xff, sizeof(iocb)); // paranoia
- free(iocb);
- write(2, "w", 1);
-}
-
-/*
- * Read complete callback.
- * Change read iocb into a write iocb and start it.
- */
-static void rd_done(io_context_t ctx, struct iocb *iocb, long res, long res2)
-{
- /* library needs accessors to look at iocb? */
- int iosize = iocb->u.c.nbytes;
- char *buf = iocb->u.c.buf;
- off_t offset = iocb->u.c.offset;
-
- if (res2 != 0)
- io_error("aio read", res2);
- if (res != iosize) {
- fprintf(stderr, "read missing bytes expect %d got %d\n", iocb->u.c.nbytes, res);
- exit(1);
- }
-
-
- /* turn read into write */
- io_prep_pwrite(iocb, dstfd, buf, iosize, offset);
- io_set_callback(iocb, wr_done);
- if (1 != (res = io_submit(ctx, 1, &iocb)))
- io_error("io_submit write", res);
- write(2, "r", 1);
-}
-
-
-int main(int argc, char *const *argv)
-{
- int srcfd;
- struct stat st;
- off_t length = 0, offset = 0;
- io_context_t myctx;
-
- if (argc != 3 || argv[1][0] == '-') {
- fprintf(stderr, "Usage: aiocp SOURCE DEST");
- exit(1);
- }
- if ((srcfd = open(srcname = argv[1], O_RDONLY)) < 0) {
- perror(srcname);
- exit(1);
- }
- if (fstat(srcfd, &st) < 0) {
- perror("fstat");
- exit(1);
- }
- length = st.st_size;
-
- if ((dstfd = open(dstname = argv[2], O_WRONLY | O_CREAT, 0666)) < 0) {
- close(srcfd);
- perror(dstname);
- exit(1);
- }
-
- /* initialize state machine */
- memset(&myctx, 0, sizeof(myctx));
- io_queue_init(AIO_MAXIO, &myctx);
- tocopy = howmany(length, AIO_BLKSIZE);
-
- while (tocopy > 0) {
- int i, rc;
- /* Submit as many reads as once as possible upto AIO_MAXIO */
- int n = MIN(MIN(AIO_MAXIO - busy, AIO_MAXIO / 2),
- howmany(length - offset, AIO_BLKSIZE));
- if (n > 0) {
- struct iocb *ioq[n];
-
- for (i = 0; i < n; i++) {
- struct iocb *io = (struct iocb *) malloc(sizeof(struct iocb));
- int iosize = MIN(length - offset, AIO_BLKSIZE);
- char *buf = (char *) malloc(iosize);
-
- if (NULL == buf || NULL == io) {
- fprintf(stderr, "out of memory\n");
- exit(1);
- }
-
- io_prep_pread(io, srcfd, buf, iosize, offset);
- io_set_callback(io, rd_done);
- ioq[i] = io;
- offset += iosize;
- }
-
- rc = io_submit(myctx, n, ioq);
- if (rc < 0)
- io_error("io_submit", rc);
-
- busy += n;
- }
-
- // Handle IO's that have completed
- rc = io_queue_run(myctx);
- if (rc < 0)
- io_error("io_queue_run", rc);
-
- // if we have maximum number of i/o's in flight
- // then wait for one to complete
- if (busy == AIO_MAXIO) {
- rc = io_queue_wait(myctx, NULL);
- if (rc < 0)
- io_error("io_queue_wait", rc);
- }
-
- }
-
- close(srcfd);
- close(dstfd);
- exit(0);
-}
-
-/*
- * Results look like:
- * [alanm@toolbox ~/MOT3]$ ../taio kernel-source-2.4.8-0.4g.ppc.rpm abc
- * rrrrrrrrrrrrrrrwwwrwrrwwrrwrwwrrwrwrwwrrwrwrrrrwwrwwwrrwrrrwwwwwwwwwwwwwwwww
- * rrrrrrrrrrrrrrwwwrrwrwrwrwrrwwwwwwwwwwwwwwrrrrrrrrrrrrrrrrrrwwwwrwrwwrwrwrwr
- * wrrrrrrrwwwwwwwwwwwwwrrrwrrrwrrwrwwwwwwwwwwrrrrwwrwrrrrrrrrrrrwwwwwwwwwwwrww
- * wwwrrrrrrrrwwrrrwwrwrwrwwwrrrrrrrwwwrrwwwrrwrwwwwwwwwrrrrrrrwwwrrrrrrrwwwwww
- * wwwwwwwrwrrrrrrrrwrrwrrwrrwrwrrrwrrrwrrrwrwwwwwwwwwwwwwwwwwwrrrwwwrrrrrrrrrr
- * rrwrrrrrrwrrwwwwwwwwwwwwwwwwrwwwrrwrwwrrrrrrrrrrrrrrrrrrrwwwwwwwwwwwwwwwwwww
- * rrrrrwrrwrwrwrrwrrrwwwwwwwwrrrrwrrrwrwwrwrrrwrrwrrrrwwwwwwwrwrwwwwrwwrrrwrrr
- * rrrwwwwwwwrrrrwwrrrrrrrrrrrrwrwrrrrwwwwwwwwwwwwwwrwrrrrwwwwrwrrrrwrwwwrrrwww
- * rwwrrrrrrrwrrrrrrrrrrrrwwwwrrrwwwrwrrwwwwwwwwwwwwwwwwwwwwwrrrrrrrwwwwwwwrw
- */
-.fi
-.SH "SEE ALSO"
-.BR io_cancel(3),
-.BR io_fsync(3),
-.BR io_getevents(3),
-.BR io_prep_fsync(3),
-.BR io_prep_pread(3),
-.BR io_prep_pwrite(3),
-.BR io_queue_init(3),
-.BR io_queue_release(3),
-.BR io_queue_run(3),
-.BR io_queue_wait(3),
-.BR io_set_callback(3),
-.BR io_submit(3),
-.BR errno(3)