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linux/arch/um/os-Linux/aio.c
Jeff Dike 09ace81c1d [PATCH] uml: add host AIO support to block driver 
This adds AIO support to the ubd driver.

The driver breaks a struct request into IO requests to the host, based on the
hardware segments in the request and on any COW blocks covered by the request.

The ubd IO thread is gone, since there is now an equivalent thread in the AIO
module.

There is provision for multiple outstanding requests now.  Requests aren't
retired until all pieces of it have been completed.  The AIO requests have a
shared count, which is decremented as IO operations come in until it reaches
0.  This can be possibly moved to the request struct - haven't looked at this
yet.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-09-05 00:06:23 -07:00

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/*
* Copyright (C) 2004 Jeff Dike (jdike@addtoit.com)
* Licensed under the GPL
*/
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <errno.h>
#include <sched.h>
#include <sys/syscall.h>
#include "os.h"
#include "helper.h"
#include "aio.h"
#include "init.h"
#include "user.h"
#include "mode.h"
static int aio_req_fd_r = -1;
static int aio_req_fd_w = -1;
static int update_aio(struct aio_context *aio, int res)
{
if(res < 0)
aio->len = res;
else if((res == 0) && (aio->type == AIO_READ)){
/* This is the EOF case - we have hit the end of the file
* and it ends in a partial block, so we fill the end of
* the block with zeros and claim success.
*/
memset(aio->data, 0, aio->len);
aio->len = 0;
}
else if(res > 0){
aio->len -= res;
aio->data += res;
aio->offset += res;
return aio->len;
}
return 0;
}
#if defined(HAVE_AIO_ABI)
#include <linux/aio_abi.h>
/* If we have the headers, we are going to build with AIO enabled.
* If we don't have aio in libc, we define the necessary stubs here.
*/
#if !defined(HAVE_AIO_LIBC)
static long io_setup(int n, aio_context_t *ctxp)
{
return syscall(__NR_io_setup, n, ctxp);
}
static long io_submit(aio_context_t ctx, long nr, struct iocb **iocbpp)
{
return syscall(__NR_io_submit, ctx, nr, iocbpp);
}
static long io_getevents(aio_context_t ctx_id, long min_nr, long nr,
struct io_event *events, struct timespec *timeout)
{
return syscall(__NR_io_getevents, ctx_id, min_nr, nr, events, timeout);
}
#endif
/* The AIO_MMAP cases force the mmapped page into memory here
* rather than in whatever place first touches the data. I used
* to do this by touching the page, but that's delicate because
* gcc is prone to optimizing that away. So, what's done here
* is we read from the descriptor from which the page was
* mapped. The caller is required to pass an offset which is
* inside the page that was mapped. Thus, when the read
* returns, we know that the page is in the page cache, and
* that it now backs the mmapped area.
*/
static int do_aio(aio_context_t ctx, struct aio_context *aio)
{
struct iocb iocb, *iocbp = &iocb;
char c;
int err;
iocb = ((struct iocb) { .aio_data = (unsigned long) aio,
.aio_reqprio = 0,
.aio_fildes = aio->fd,
.aio_buf = (unsigned long) aio->data,
.aio_nbytes = aio->len,
.aio_offset = aio->offset,
.aio_reserved1 = 0,
.aio_reserved2 = 0,
.aio_reserved3 = 0 });
switch(aio->type){
case AIO_READ:
iocb.aio_lio_opcode = IOCB_CMD_PREAD;
break;
case AIO_WRITE:
iocb.aio_lio_opcode = IOCB_CMD_PWRITE;
break;
case AIO_MMAP:
iocb.aio_lio_opcode = IOCB_CMD_PREAD;
iocb.aio_buf = (unsigned long) &c;
iocb.aio_nbytes = sizeof(c);
break;
default:
printk("Bogus op in do_aio - %d\n", aio->type);
err = -EINVAL;
goto out;
}
err = io_submit(ctx, 1, &iocbp);
if(err > 0)
err = 0;
out:
return err;
}
static aio_context_t ctx = 0;
static int aio_thread(void *arg)
{
struct aio_thread_reply reply;
struct aio_context *aio;
struct io_event event;
int err, n;
signal(SIGWINCH, SIG_IGN);
while(1){
n = io_getevents(ctx, 1, 1, &event, NULL);
if(n < 0){
if(errno == EINTR)
continue;
printk("aio_thread - io_getevents failed, "
"errno = %d\n", errno);
}
else {
aio = (struct aio_context *) event.data;
if(update_aio(aio, event.res)){
do_aio(ctx, aio);
continue;
}
reply = ((struct aio_thread_reply)
{ .data = aio,
.err = aio->len });
err = os_write_file(aio->reply_fd, &reply,
sizeof(reply));
if(err != sizeof(reply))
printk("aio_thread - write failed, "
"fd = %d, err = %d\n", aio->reply_fd,
-err);
}
}
return 0;
}
#endif
static int do_not_aio(struct aio_context *aio)
{
char c;
int err;
switch(aio->type){
case AIO_READ:
err = os_seek_file(aio->fd, aio->offset);
if(err)
goto out;
err = os_read_file(aio->fd, aio->data, aio->len);
break;
case AIO_WRITE:
err = os_seek_file(aio->fd, aio->offset);
if(err)
goto out;
err = os_write_file(aio->fd, aio->data, aio->len);
break;
case AIO_MMAP:
err = os_seek_file(aio->fd, aio->offset);
if(err)
goto out;
err = os_read_file(aio->fd, &c, sizeof(c));
break;
default:
printk("do_not_aio - bad request type : %d\n", aio->type);
err = -EINVAL;
break;
}
out:
return err;
}
static int not_aio_thread(void *arg)
{
struct aio_context *aio;
struct aio_thread_reply reply;
int err;
signal(SIGWINCH, SIG_IGN);
while(1){
err = os_read_file(aio_req_fd_r, &aio, sizeof(aio));
if(err != sizeof(aio)){
if(err < 0)
printk("not_aio_thread - read failed, "
"fd = %d, err = %d\n", aio_req_fd_r,
-err);
else {
printk("not_aio_thread - short read, fd = %d, "
"length = %d\n", aio_req_fd_r, err);
}
continue;
}
again:
err = do_not_aio(aio);
if(update_aio(aio, err))
goto again;
reply = ((struct aio_thread_reply) { .data = aio,
.err = aio->len });
err = os_write_file(aio->reply_fd, &reply, sizeof(reply));
if(err != sizeof(reply))
printk("not_aio_thread - write failed, fd = %d, "
"err = %d\n", aio_req_fd_r, -err);
}
}
static int submit_aio_24(struct aio_context *aio)
{
int err;
err = os_write_file(aio_req_fd_w, &aio, sizeof(aio));
if(err == sizeof(aio))
err = 0;
return err;
}
static int aio_pid = -1;
static int (*submit_proc)(struct aio_context *aio);
static int init_aio_24(void)
{
unsigned long stack;
int fds[2], err;
err = os_pipe(fds, 1, 1);
if(err)
goto out;
aio_req_fd_w = fds[0];
aio_req_fd_r = fds[1];
err = run_helper_thread(not_aio_thread, NULL,
CLONE_FILES | CLONE_VM | SIGCHLD, &stack, 0);
if(err < 0)
goto out_close_pipe;
aio_pid = err;
goto out;
out_close_pipe:
os_close_file(fds[0]);
os_close_file(fds[1]);
aio_req_fd_w = -1;
aio_req_fd_r = -1;
out:
#ifndef HAVE_AIO_ABI
printk("/usr/include/linux/aio_abi.h not present during build\n");
#endif
printk("2.6 host AIO support not used - falling back to I/O "
"thread\n");
submit_proc = submit_aio_24;
return 0;
}
#ifdef HAVE_AIO_ABI
#define DEFAULT_24_AIO 0
static int submit_aio_26(struct aio_context *aio)
{
struct aio_thread_reply reply;
int err;
err = do_aio(ctx, aio);
if(err){
reply = ((struct aio_thread_reply) { .data = aio,
.err = err });
err = os_write_file(aio->reply_fd, &reply, sizeof(reply));
if(err != sizeof(reply))
printk("submit_aio_26 - write failed, "
"fd = %d, err = %d\n", aio->reply_fd, -err);
else err = 0;
}
return err;
}
static int init_aio_26(void)
{
unsigned long stack;
int err;
if(io_setup(256, &ctx)){
printk("aio_thread failed to initialize context, err = %d\n",
errno);
return -errno;
}
err = run_helper_thread(aio_thread, NULL,
CLONE_FILES | CLONE_VM | SIGCHLD, &stack, 0);
if(err < 0)
return -errno;
aio_pid = err;
printk("Using 2.6 host AIO\n");
submit_proc = submit_aio_26;
return 0;
}
#else
#define DEFAULT_24_AIO 1
static int submit_aio_26(struct aio_context *aio)
{
return -ENOSYS;
}
static int init_aio_26(void)
{
submit_proc = submit_aio_26;
return -ENOSYS;
}
#endif
static int aio_24 = DEFAULT_24_AIO;
static int __init set_aio_24(char *name, int *add)
{
aio_24 = 1;
return 0;
}
__uml_setup("aio=2.4", set_aio_24,
"aio=2.4\n"
" This is used to force UML to use 2.4-style AIO even when 2.6 AIO is\n"
" available. 2.4 AIO is a single thread that handles one request at a\n"
" time, synchronously. 2.6 AIO is a thread which uses the 2.6 AIO \n"
" interface to handle an arbitrary number of pending requests. 2.6 AIO \n"
" is not available in tt mode, on 2.4 hosts, or when UML is built with\n"
" /usr/include/linux/aio_abi.h not available. Many distributions don't\n"
" include aio_abi.h, so you will need to copy it from a kernel tree to\n"
" your /usr/include/linux in order to build an AIO-capable UML\n\n"
);
static int init_aio(void)
{
int err;
CHOOSE_MODE(({
if(!aio_24){
printk("Disabling 2.6 AIO in tt mode\n");
aio_24 = 1;
} }), (void) 0);
if(!aio_24){
err = init_aio_26();
if(err && (errno == ENOSYS)){
printk("2.6 AIO not supported on the host - "
"reverting to 2.4 AIO\n");
aio_24 = 1;
}
else return err;
}
if(aio_24)
return init_aio_24();
return 0;
}
/* The reason for the __initcall/__uml_exitcall asymmetry is that init_aio
* needs to be called when the kernel is running because it calls run_helper,
* which needs get_free_page. exit_aio is a __uml_exitcall because the generic
* kernel does not run __exitcalls on shutdown, and can't because many of them
* break when called outside of module unloading.
*/
__initcall(init_aio);
static void exit_aio(void)
{
if(aio_pid != -1)
os_kill_process(aio_pid, 1);
}
__uml_exitcall(exit_aio);
int submit_aio(struct aio_context *aio)
{
return (*submit_proc)(aio);
}
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