svn commit: r303164 - in head: lib/libc/sys share/man/man4 sys/kern
John Baldwin
jhb at FreeBSD.org
Thu Jul 21 22:49:49 UTC 2016
Author: jhb
Date: Thu Jul 21 22:49:47 2016
New Revision: 303164
URL: https://svnweb.freebsd.org/changeset/base/303164
Log:
Add more documentation regarding unsafe AIO requests.
The asynchronous I/O changes made previously result in different
behavior out of the box. Previously all AIO requests failed with
ENOSYS / SIGSYS unless aio.ko was explicitly loaded. Now, some AIO
requests complete and others ("unsafe" requests) fail with EOPNOTSUPP.
Reword the introductory paragraph in aio(4) to add a general
description of AIO before describing the vfs.aio.enable_unsafe sysctl.
Remove the ENOSYS error description from aio_fsync(2), aio_read(2),
and aio_write(2) and replace it with a description of EOPNOTSUPP.
Remove the ENOSYS error description from aio_mlock(2).
Log a message to the system log the first time a process requests an
"unsafe" AIO request that fails with EOPNOTSUPP. This is modeled on
the log message used for processes using the legacy pty devices.
Reviewed by: kib (earlier version)
MFC after: 1 week
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D7151
Modified:
head/lib/libc/sys/aio_fsync.2
head/lib/libc/sys/aio_mlock.2
head/lib/libc/sys/aio_read.2
head/lib/libc/sys/aio_write.2
head/share/man/man4/aio.4
head/sys/kern/vfs_aio.c
Modified: head/lib/libc/sys/aio_fsync.2
==============================================================================
--- head/lib/libc/sys/aio_fsync.2 Thu Jul 21 22:13:40 2016 (r303163)
+++ head/lib/libc/sys/aio_fsync.2 Thu Jul 21 22:49:47 2016 (r303164)
@@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd July 15, 2016
+.Dd July 21, 2016
.Dt AIO_FSYNC 2
.Os
.Sh NAME
@@ -107,10 +107,10 @@ The request was not queued because of sy
The asynchronous notification method in
.Fa iocb->aio_sigevent.sigev_notify
is invalid or not supported.
-.It Bq Er ENOSYS
-The
-.Fn aio_fsync
-system call is not supported.
+.It Bq Er EOPNOTSUPP
+Asynchronous file synchronization operations on the file descriptor
+.Fa iocb->aio_fildes
+are unsafe and unsafe asynchronous I/O operations are disabled.
.It Bq Er EINVAL
A value of the
.Fa op
Modified: head/lib/libc/sys/aio_mlock.2
==============================================================================
--- head/lib/libc/sys/aio_mlock.2 Thu Jul 21 22:13:40 2016 (r303163)
+++ head/lib/libc/sys/aio_mlock.2 Thu Jul 21 22:49:47 2016 (r303164)
@@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd July 15, 2016
+.Dd July 21, 2016
.Dt AIO_MLOCK 2
.Os
.Sh NAME
@@ -102,10 +102,6 @@ The request was not queued because of sy
The asynchronous notification method in
.Fa iocb->aio_sigevent.sigev_notify
is invalid or not supported.
-.It Bq Er ENOSYS
-The
-.Fn aio_mlock
-system call is not supported.
.El
.Pp
If the request is successfully enqueued, but subsequently cancelled
Modified: head/lib/libc/sys/aio_read.2
==============================================================================
--- head/lib/libc/sys/aio_read.2 Thu Jul 21 22:13:40 2016 (r303163)
+++ head/lib/libc/sys/aio_read.2 Thu Jul 21 22:49:47 2016 (r303164)
@@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd July 15, 2016
+.Dd July 21, 2016
.Dt AIO_READ 2
.Os
.Sh NAME
@@ -125,10 +125,10 @@ The request was not queued because of sy
The asynchronous notification method in
.Fa iocb->aio_sigevent.sigev_notify
is invalid or not supported.
-.It Bq Er ENOSYS
-The
-.Fn aio_read
-system call is not supported.
+.It Bq Er EOPNOTSUPP
+Asynchronous read operations on the file descriptor
+.Fa iocb->aio_fildes
+are unsafe and unsafe asynchronous I/O operations are disabled.
.El
.Pp
The following conditions may be synchronously detected when the
Modified: head/lib/libc/sys/aio_write.2
==============================================================================
--- head/lib/libc/sys/aio_write.2 Thu Jul 21 22:13:40 2016 (r303163)
+++ head/lib/libc/sys/aio_write.2 Thu Jul 21 22:49:47 2016 (r303164)
@@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd July 15, 2016
+.Dd July 21, 2016
.Dt AIO_WRITE 2
.Os
.Sh NAME
@@ -129,10 +129,10 @@ The request was not queued because of sy
The asynchronous notification method in
.Fa iocb->aio_sigevent.sigev_notify
is invalid or not supported.
-.It Bq Er ENOSYS
-The
-.Fn aio_write
-system call is not supported.
+.It Bq Er EOPNOTSUPP
+Asynchronous write operations on the file descriptor
+.Fa iocb->aio_fildes
+are unsafe and unsafe asynchronous I/O operations are disabled.
.El
.Pp
The following conditions may be synchronously detected when the
Modified: head/share/man/man4/aio.4
==============================================================================
--- head/share/man/man4/aio.4 Thu Jul 21 22:13:40 2016 (r303163)
+++ head/share/man/man4/aio.4 Thu Jul 21 22:49:47 2016 (r303164)
@@ -27,7 +27,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd July 15, 2016
+.Dd July 21, 2016
.Dt AIO 4
.Os
.Sh NAME
@@ -37,17 +37,25 @@
The
.Nm
facility provides system calls for asynchronous I/O.
-However, asynchronous I/O operations are only enabled for certain file
-types by default.
-Asynchronous I/O operations for other file types may block an AIO daemon
-indefinitely resulting in process and/or system hangs.
-Asynchronous I/O operations can be enabled for all file types by setting
+Asynchronous I/O operations are not completed synchronously by the
+calling thread.
+Instead, the calling thread invokes one system call to request an
+asynchronous I/O operation.
+The status of a completed request is retrieved later via a separate
+system call.
+.Pp
+Asynchronous I/O operations on some file descriptor types may block an
+AIO daemon indefinitely resulting in process and/or system hangs.
+Operations on these file descriptor types are considered
+.Dq unsafe
+and disabled by default.
+They can be enabled by setting
the
.Va vfs.aio.enable_unsafe
sysctl node to a non-zero value.
.Pp
Asynchronous I/O operations on sockets and raw disk devices do not block
-indefinitely and are enabled by default.
+indefinitely and are always enabled.
.Pp
The
.Nm
Modified: head/sys/kern/vfs_aio.c
==============================================================================
--- head/sys/kern/vfs_aio.c Thu Jul 21 22:13:40 2016 (r303163)
+++ head/sys/kern/vfs_aio.c Thu Jul 21 22:49:47 2016 (r303164)
@@ -53,6 +53,7 @@ __FBSDID("$FreeBSD$");
#include <sys/syscall.h>
#include <sys/sysent.h>
#include <sys/sysctl.h>
+#include <sys/syslog.h>
#include <sys/sx.h>
#include <sys/taskqueue.h>
#include <sys/vnode.h>
@@ -110,6 +111,11 @@ static int enable_aio_unsafe = 0;
SYSCTL_INT(_vfs_aio, OID_AUTO, enable_unsafe, CTLFLAG_RW, &enable_aio_unsafe, 0,
"Permit asynchronous IO on all file types, not just known-safe types");
+static unsigned int unsafe_warningcnt = 1;
+SYSCTL_UINT(_vfs_aio, OID_AUTO, unsafe_warningcnt, CTLFLAG_RW,
+ &unsafe_warningcnt, 0,
+ "Warnings that will be triggered upon failed IO requests on unsafe files");
+
static int max_aio_procs = MAX_AIO_PROCS;
SYSCTL_INT(_vfs_aio, OID_AUTO, max_aio_procs, CTLFLAG_RW, &max_aio_procs, 0,
"Maximum number of kernel processes to use for handling async IO ");
@@ -1697,8 +1703,11 @@ queueit:
safe = true;
}
}
- if (!(safe || enable_aio_unsafe))
+ if (!(safe || enable_aio_unsafe)) {
+ counted_warning(&unsafe_warningcnt,
+ "is attempting to use unsafe AIO requests");
return (EOPNOTSUPP);
+ }
if (opcode == LIO_SYNC) {
AIO_LOCK(ki);
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