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| author | jhb <jhb@FreeBSD.org> | 2016-07-28 20:31:30 +0000 |
|---|---|---|
| committer | jhb <jhb@FreeBSD.org> | 2016-07-28 20:31:30 +0000 |
| commit | 9b2ba0e5df123933210b18da17ec3ca2d5f5c41a (patch) | |
| tree | 6047b7259e2553745848f83a2183fd0e536ddb1f /share | |
| parent | e442a085d06ea3acc1ac496469c4e212774a2c5d (diff) | |
| download | FreeBSD-src-9b2ba0e5df123933210b18da17ec3ca2d5f5c41a.zip FreeBSD-src-9b2ba0e5df123933210b18da17ec3ca2d5f5c41a.tar.gz | |
MFC 303164: 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.
Approved by: re (gjb)
Diffstat (limited to 'share')
| -rw-r--r-- | share/man/man4/aio.4 | 22 |
1 files changed, 15 insertions, 7 deletions
diff --git a/share/man/man4/aio.4 b/share/man/man4/aio.4 index 460b3c8..efcfe24 100644 --- a/share/man/man4/aio.4 +++ b/share/man/man4/aio.4 @@ -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 |
