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Add more documentation regarding unsafe AIO requests.

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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
This commit is contained in:
John Baldwin 2016-07-21 22:49:47 +00:00
parent e0633de05a
commit 9c20dc9963
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=303164
6 changed files with 41 additions and 28 deletions
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10
lib/libc/sys/aio_fsync.2
View File

@ -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 system resource limitations.
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

6
lib/libc/sys/aio_mlock.2
View File

@ -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 system resource limitations.
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

10
lib/libc/sys/aio_read.2
View File

@ -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 system resource limitations.
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

10
lib/libc/sys/aio_write.2
View File

@ -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 system resource limitations.
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

22
share/man/man4/aio.4
View File

@ -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

11
sys/kern/vfs_aio.c
View File

@ -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 @@ aio_queue_file(struct file *fp, struct kaiocb *job)
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);