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[Xen-devel] [PATCH 4 of 4] blktap2: Prefer AIO eventfd support on kernel

To: Xen <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] [PATCH 4 of 4] blktap2: Prefer AIO eventfd support on kernels >= 2.6.22
From: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Date: Fri, 29 Jan 2010 07:44:27 -0000
Delivery-date: Thu, 28 Jan 2010 23:50:04 -0800
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# HG changeset patch
# User Daniel Stodden <dns@xxxxxxxxxxxx>
# Date 1264750223 28800
# Node ID 1e60fec876f2254b62ebc052fe4eb3ce96c016d4
# Parent  2b8c81d25096575472974f1e81829b73f0fe7d69
blktap2: Prefer AIO eventfd support on kernels >= 2.6.22

Mainline kernel support for eventfd(2) in linux aio was added between
2.6.21 and 2.6.22. Libaio after 0.3.107 has the header file, but
presently few systems support it. Neither do we rely on an up-to-date
libc6.

Instead, this patch adds a header which defines custom iocb_common
struct, and works around a potentially missing sys/eventfd.h.

Signed-off-by: Daniel Stodden <daniel.stodden@xxxxxxxxxx>

diff -r 2b8c81d25096 -r 1e60fec876f2 tools/blktap2/drivers/block-aio.c
--- a/tools/blktap2/drivers/block-aio.c Thu Jan 28 23:30:23 2010 -0800
+++ b/tools/blktap2/drivers/block-aio.c Thu Jan 28 23:30:23 2010 -0800
@@ -28,7 +28,6 @@
 
 
 #include <errno.h>
-#include <libaio.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
diff -r 2b8c81d25096 -r 1e60fec876f2 tools/blktap2/drivers/libaio-compat.h
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/tools/blktap2/drivers/libaio-compat.h     Thu Jan 28 23:30:23 2010 -0800
@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) 2010, XenSource Inc.
+ * All rights reserved.
+ *
+ * This  library is  free  software; you  can  redistribute it  and/or
+ * modify it under the terms  of the GNU Lesser General Public License
+ * as published by  the Free Software Foundation; either  version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful, but
+ * WITHOUT  ANY  WARRANTY;  without   even  the  implied  warranty  of
+ * MERCHANTABILITY or  FITNESS FOR A PARTICULAR PURPOSE.   See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should  have received a copy  of the GNU  Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+ * USA
+ */
+
+/*
+ * kernel 2.6.21 added eventfd(2) support, kernel 2.6.22 eventfds for
+ * aio. libaio 0.3.107 updated the header file, but few systems have
+ * it. define a custom iocb_common struct instead, and work around a
+ * potentially missing sys/eventfd.h. this header should vanish over
+ * time.
+ */
+
+#ifndef __LIBAIO_COMPAT
+#define __LIBAIO_COMPAT
+
+#include <libaio.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+
+struct __compat_io_iocb_common {
+       char             __pad_buf[8];
+       char             __pad_nbytes[8];
+       long long       offset;
+       long long       __pad3;
+       unsigned        flags;
+       unsigned        resfd;
+};
+
+static inline void __io_set_eventfd(struct iocb *iocb, int eventfd)
+{
+       struct __compat_io_iocb_common *c;
+       c = (struct __compat_io_iocb_common*)&iocb->u.c;
+       c->flags |= (1 << 0);
+       c->resfd = eventfd;
+}
+
+#ifndef SYS_eventfd
+#ifndef __NR_eventfd
+# if defined(__alpha__)
+#  define __NR_eventfd         478
+# elif defined(__arm__)
+#  define __NR_eventfd         (__NR_SYSCALL_BASE+351)
+# elif defined(__ia64__)
+#  define __NR_eventfd         1309
+# elif defined(__i386__)
+#  define __NR_eventfd         323
+# elif defined(__m68k__)
+#  define __NR_eventfd         319
+# elif 0 && defined(__mips__)
+#  error __NR_eventfd?
+#  define __NR_eventfd         (__NR_Linux + 319)
+#  define __NR_eventfd         (__NR_Linux + 278)
+#  define __NR_eventfd         (__NR_Linux + 282)
+# elif defined(__hppa__)
+#  define __NR_eventfd         (__NR_Linux + 304)
+# elif defined(__PPC__) || defined(__powerpc64__)
+#  define __NR_eventfd         307
+# elif defined(__s390__) || defined(__s390x__)
+#  define __NR_eventfd         318
+# elif defined(__sparc__)
+#  define __NR_eventfd         313
+# elif defined(__x86_64__)
+#  define __NR_eventfd         284
+# endif
+#else
+# error __NR_eventfd?
+#endif
+#define SYS_eventfd __NR_eventfd
+#endif
+
+static inline int tapdisk_sys_eventfd(int initval)
+{
+       return syscall(SYS_eventfd, initval, 0);
+}
+
+#endif /* __LIBAIO_COMPAT */
diff -r 2b8c81d25096 -r 1e60fec876f2 tools/blktap2/drivers/tapdisk-queue.c
--- a/tools/blktap2/drivers/tapdisk-queue.c     Thu Jan 28 23:30:23 2010 -0800
+++ b/tools/blktap2/drivers/tapdisk-queue.c     Thu Jan 28 23:30:23 2010 -0800
@@ -30,12 +30,18 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <libaio.h>
+#ifdef __linux__
+#include <linux/version.h>
+#endif
 
 #include "tapdisk.h"
 #include "tapdisk-log.h"
 #include "tapdisk-queue.h"
 #include "tapdisk-filter.h"
 #include "tapdisk-server.h"
+#include "tapdisk-utils.h"
+
+#include "libaio-compat.h"
 #include "atomicio.h"
 
 #define WARN(_f, _a...) tlog_write(TLOG_WARN, _f, ##_a)
@@ -270,10 +276,122 @@
        io_context_t     aio_ctx;
        struct io_event *aio_events;
 
-       int              poll_fd;
+       int              event_fd;
        int              event_id;
+
+       int              flags;
 };
 
+#define LIO_FLAG_EVENTFD        (1<<0)
+
+static int
+tapdisk_lio_check_resfd(void)
+{
+       return tapdisk_linux_version() >= KERNEL_VERSION(2, 6, 22);
+}
+
+static void
+tapdisk_lio_destroy_aio(struct tqueue *queue)
+{
+       struct lio *lio = queue->tio_data;
+
+       if (lio->event_fd >= 0) {
+               close(lio->event_fd);
+               lio->event_fd = -1;
+       }
+
+       if (lio->aio_ctx) {
+               io_destroy(lio->aio_ctx);
+               lio->aio_ctx = 0;
+       }
+}
+
+static int
+__lio_setup_aio_poll(struct tqueue *queue, int qlen)
+{
+       struct lio *lio = queue->tio_data;
+       int err, fd;
+
+       lio->aio_ctx = REQUEST_ASYNC_FD;
+
+       fd = io_setup(qlen, &lio->aio_ctx);
+       if (fd < 0) {
+               lio->aio_ctx = 0;
+               err = -errno;
+
+               if (err == -EINVAL)
+                       goto fail_fd;
+
+               goto fail;
+       }
+
+       lio->event_fd = fd;
+
+       return 0;
+
+fail_fd:
+       DPRINTF("Couldn't get fd for AIO poll support. This is probably "
+               "because your kernel does not have the aio-poll patch "
+               "applied.\n");
+fail:
+       return err;
+}
+
+static int
+__lio_setup_aio_eventfd(struct tqueue *queue, int qlen)
+{
+       struct lio *lio = queue->tio_data;
+       int err;
+
+       err = io_setup(qlen, &lio->aio_ctx);
+       if (err < 0) {
+               lio->aio_ctx = 0;
+               return err;
+       }
+
+       lio->event_fd = tapdisk_sys_eventfd(0);
+       if (lio->event_fd < 0)
+               return  -errno;
+
+       lio->flags |= LIO_FLAG_EVENTFD;
+
+       return 0;
+}
+
+static int
+tapdisk_lio_setup_aio(struct tqueue *queue, int qlen)
+{
+       struct lio *lio = queue->tio_data;
+       int err;
+
+       lio->aio_ctx  =  0;
+       lio->event_fd = -1;
+
+       /*
+        * prefer the mainline eventfd(2) api, if available.
+        * if not, fall back to the poll fd patch.
+        */
+
+       err = !tapdisk_lio_check_resfd();
+       if (!err)
+               err = __lio_setup_aio_eventfd(queue, qlen);
+       if (err)
+               err = __lio_setup_aio_poll(queue, qlen);
+
+       if (err == -EAGAIN)
+               goto fail_rsv;
+fail:
+       return err;
+
+fail_rsv:
+       DPRINTF("Couldn't setup AIO context. If you are trying to "
+               "concurrently use a large number of blktap-based disks, you may 
"
+               "need to increase the system-wide aio request limit. "
+               "(e.g. 'echo 1048576 > /proc/sys/fs/aio-max-nr')\n");
+       goto fail;
+}
+
+
 static void
 tapdisk_lio_destroy(struct tqueue *queue)
 {
@@ -287,10 +405,7 @@
                lio->event_id = -1;
        }
 
-       if (lio->aio_ctx) {
-               io_destroy(lio->aio_ctx);
-               lio->aio_ctx = NULL;
-       }
+       tapdisk_lio_destroy_aio(queue);
 
        if (lio->aio_events) {
                free(lio->aio_events);
@@ -299,6 +414,27 @@
 }
 
 static void
+tapdisk_lio_set_eventfd(struct tqueue *queue, int n, struct iocb **iocbs)
+{
+       struct lio *lio = queue->tio_data;
+       int i;
+
+       if (lio->flags & LIO_FLAG_EVENTFD)
+               for (i = 0; i < n; ++i)
+                       __io_set_eventfd(iocbs[i], lio->event_fd);
+}
+
+static void
+tapdisk_lio_ack_event(struct tqueue *queue)
+{
+       struct lio *lio = queue->tio_data;
+       uint64_t val;
+
+       if (lio->flags & LIO_FLAG_EVENTFD)
+               read(lio->event_fd, &val, sizeof(val));
+}
+
+static void
 tapdisk_lio_event(event_id_t id, char mode, void *private)
 {
        struct tqueue *queue = private;
@@ -308,6 +444,8 @@
        struct tiocb *tiocb;
        struct io_event *ep;
 
+       tapdisk_lio_ack_event(queue);
+
        lio   = queue->tio_data;
        ret   = io_getevents(lio->aio_ctx, 0,
                             queue->size, lio->aio_events, NULL);
@@ -336,22 +474,14 @@
        int err;
 
        lio->event_id = -1;
-       lio->aio_ctx  = REQUEST_ASYNC_FD;
 
-       lio->poll_fd = io_setup(qlen, &lio->aio_ctx);
-       err = lio->poll_fd;
-       if (err < 0) {
-               lio->aio_ctx = NULL;
-
-               if (err == -EAGAIN)
-                       goto fail_rsv;
-
-               goto fail_fd;
-       }
+       err = tapdisk_lio_setup_aio(queue, qlen);
+       if (err)
+               goto fail;
 
        lio->event_id =
                tapdisk_server_register_event(SCHEDULER_POLL_READ_FD,
-                                             lio->poll_fd, 0,
+                                             lio->event_fd, 0,
                                              tapdisk_lio_event,
                                              queue);
        err = lio->event_id;
@@ -369,19 +499,6 @@
 fail:
        tapdisk_lio_destroy(queue);
        return err;
-
-fail_rsv:
-       DPRINTF("Couldn't setup AIO context. If you are trying to "
-               "concurrently use a large number of blktap-based disks, you may 
"
-               "need to increase the system-wide aio request limit. "
-               "(e.g. 'echo 1048576 > /proc/sys/fs/aio-max-nr')\n");
-       goto fail;
-
-fail_fd:
-       DPRINTF("Couldn't get fd for AIO poll support. This is probably "
-               "because your kernel does not have  the aio-poll patch "
-               "applied.\n");
-       goto fail;
 }
 
 static int
@@ -395,6 +512,7 @@
 
        tapdisk_filter_iocbs(queue->filter, queue->iocbs, queue->queued);
        merged    = io_merge(&queue->opioctx, queue->iocbs, queue->queued);
+       tapdisk_lio_set_eventfd(queue, merged, queue->iocbs);
        submitted = io_submit(lio->aio_ctx, merged, queue->iocbs);
 
        DBG("queued: %d, merged: %d, submitted: %d\n",
diff -r 2b8c81d25096 -r 1e60fec876f2 tools/blktap2/drivers/tapdisk-utils.c
--- a/tools/blktap2/drivers/tapdisk-utils.c     Thu Jan 28 23:30:23 2010 -0800
+++ b/tools/blktap2/drivers/tapdisk-utils.c     Thu Jan 28 23:30:23 2010 -0800
@@ -33,6 +33,10 @@
 #include <sys/mman.h>
 #include <sys/ioctl.h>
 #include <sys/resource.h>
+#include <sys/utsname.h>
+#ifdef __linux__
+#include <linux/version.h>
+#endif
 
 #include "blk.h"
 #include "tapdisk.h"
@@ -183,3 +187,31 @@
 
        return 0;
 }
+
+#ifdef __linux__
+
+int tapdisk_linux_version(void)
+{
+       struct utsname uts;
+       unsigned int version, patchlevel, sublevel;
+       int n, err;
+
+       err = uname(&uts);
+       if (err)
+               return -errno;
+
+       n = sscanf(uts.release, "%u.%u.%u", &version, &patchlevel, &sublevel);
+       if (n != 3)
+               return -ENOSYS;
+
+       return KERNEL_VERSION(version, patchlevel, sublevel);
+}
+
+#else
+
+int tapdisk_linux_version(void)
+{
+       return -ENOSYS;
+}
+
+#endif
diff -r 2b8c81d25096 -r 1e60fec876f2 tools/blktap2/drivers/tapdisk-utils.h
--- a/tools/blktap2/drivers/tapdisk-utils.h     Thu Jan 28 23:30:23 2010 -0800
+++ b/tools/blktap2/drivers/tapdisk-utils.h     Thu Jan 28 23:30:23 2010 -0800
@@ -38,5 +38,6 @@
 int tapdisk_namedup(char **, const char *);
 int tapdisk_parse_disk_type(const char *, char **, int *);
 int tapdisk_get_image_size(int, uint64_t *, uint32_t *);
+int tapdisk_linux_version(void);
 
 #endif
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