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
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2020-12-20 02:59:44 +00:00
svn path=/head/; revision=303164
@ -24,7 +24,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 15, 2016
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.Dd July 21, 2016
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.Dt AIO_FSYNC 2
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.Os
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.Sh NAME
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@ -107,10 +107,10 @@ The request was not queued because of system resource limitations.
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The asynchronous notification method in
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.Fa iocb->aio_sigevent.sigev_notify
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is invalid or not supported.
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.It Bq Er ENOSYS
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The
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.Fn aio_fsync
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system call is not supported.
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.It Bq Er EOPNOTSUPP
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Asynchronous file synchronization operations on the file descriptor
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.Fa iocb->aio_fildes
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are unsafe and unsafe asynchronous I/O operations are disabled.
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.It Bq Er EINVAL
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A value of the
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.Fa op
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@ -24,7 +24,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 15, 2016
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.Dd July 21, 2016
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.Dt AIO_MLOCK 2
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.Os
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.Sh NAME
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@ -102,10 +102,6 @@ The request was not queued because of system resource limitations.
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The asynchronous notification method in
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.Fa iocb->aio_sigevent.sigev_notify
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is invalid or not supported.
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.It Bq Er ENOSYS
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The
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.Fn aio_mlock
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system call is not supported.
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.El
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.Pp
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If the request is successfully enqueued, but subsequently cancelled
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@ -24,7 +24,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 15, 2016
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.Dd July 21, 2016
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.Dt AIO_READ 2
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.Os
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.Sh NAME
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@ -125,10 +125,10 @@ The request was not queued because of system resource limitations.
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The asynchronous notification method in
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.Fa iocb->aio_sigevent.sigev_notify
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is invalid or not supported.
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.It Bq Er ENOSYS
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The
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.Fn aio_read
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system call is not supported.
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.It Bq Er EOPNOTSUPP
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Asynchronous read operations on the file descriptor
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.Fa iocb->aio_fildes
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are unsafe and unsafe asynchronous I/O operations are disabled.
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.El
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.Pp
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The following conditions may be synchronously detected when the
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@ -24,7 +24,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 15, 2016
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.Dd July 21, 2016
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.Dt AIO_WRITE 2
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.Os
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.Sh NAME
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@ -129,10 +129,10 @@ The request was not queued because of system resource limitations.
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The asynchronous notification method in
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.Fa iocb->aio_sigevent.sigev_notify
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is invalid or not supported.
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.It Bq Er ENOSYS
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The
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.Fn aio_write
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system call is not supported.
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.It Bq Er EOPNOTSUPP
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Asynchronous write operations on the file descriptor
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.Fa iocb->aio_fildes
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are unsafe and unsafe asynchronous I/O operations are disabled.
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.El
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.Pp
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The following conditions may be synchronously detected when the
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@ -27,7 +27,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 15, 2016
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.Dd July 21, 2016
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.Dt AIO 4
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.Os
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.Sh NAME
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@ -37,17 +37,25 @@
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The
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.Nm
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facility provides system calls for asynchronous I/O.
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However, asynchronous I/O operations are only enabled for certain file
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types by default.
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Asynchronous I/O operations for other file types may block an AIO daemon
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indefinitely resulting in process and/or system hangs.
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Asynchronous I/O operations can be enabled for all file types by setting
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Asynchronous I/O operations are not completed synchronously by the
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calling thread.
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Instead, the calling thread invokes one system call to request an
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asynchronous I/O operation.
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The status of a completed request is retrieved later via a separate
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system call.
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.Pp
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Asynchronous I/O operations on some file descriptor types may block an
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AIO daemon indefinitely resulting in process and/or system hangs.
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Operations on these file descriptor types are considered
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.Dq unsafe
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and disabled by default.
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They can be enabled by setting
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the
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.Va vfs.aio.enable_unsafe
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sysctl node to a non-zero value.
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.Pp
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Asynchronous I/O operations on sockets and raw disk devices do not block
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indefinitely and are enabled by default.
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indefinitely and are always enabled.
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.Pp
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The
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.Nm
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@ -53,6 +53,7 @@ __FBSDID("$FreeBSD$");
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#include <sys/syscall.h>
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#include <sys/sysent.h>
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#include <sys/sysctl.h>
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#include <sys/syslog.h>
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#include <sys/sx.h>
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#include <sys/taskqueue.h>
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#include <sys/vnode.h>
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@ -110,6 +111,11 @@ static int enable_aio_unsafe = 0;
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SYSCTL_INT(_vfs_aio, OID_AUTO, enable_unsafe, CTLFLAG_RW, &enable_aio_unsafe, 0,
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"Permit asynchronous IO on all file types, not just known-safe types");
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static unsigned int unsafe_warningcnt = 1;
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SYSCTL_UINT(_vfs_aio, OID_AUTO, unsafe_warningcnt, CTLFLAG_RW,
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&unsafe_warningcnt, 0,
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"Warnings that will be triggered upon failed IO requests on unsafe files");
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static int max_aio_procs = MAX_AIO_PROCS;
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SYSCTL_INT(_vfs_aio, OID_AUTO, max_aio_procs, CTLFLAG_RW, &max_aio_procs, 0,
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"Maximum number of kernel processes to use for handling async IO ");
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@ -1697,8 +1703,11 @@ aio_queue_file(struct file *fp, struct kaiocb *job)
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safe = true;
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}
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}
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if (!(safe || enable_aio_unsafe))
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if (!(safe || enable_aio_unsafe)) {
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counted_warning(&unsafe_warningcnt,
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"is attempting to use unsafe AIO requests");
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return (EOPNOTSUPP);
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}
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if (opcode == LIO_SYNC) {
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AIO_LOCK(ki);
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