Date: Thu, 21 Jul 2016 22:49:47 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r303164 - in head: lib/libc/sys share/man/man4 sys/kern Message-ID: <201607212249.u6LMnlEJ076651@repo.freebsd.org>
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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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