Refactor the AIO subsystem to permit file-type-specific handling and

improve cancellation robustness.

Introduce a new file operation, fo_aio_queue, which is responsible for
queueing and completing an asynchronous I/O request for a given file.
The AIO subystem now exports library of routines to manipulate AIO
requests as well as the ability to run a handler function in the
"default" pool of AIO daemons to service a request.

A default implementation for file types which do not include an
fo_aio_queue method queues requests to the "default" pool invoking the
fo_read or fo_write methods as before.

The AIO subsystem permits file types to install a private "cancel"
routine when a request is queued to permit safe dequeueing and cleanup
of cancelled requests.

Sockets now use their own pool of AIO daemons and service per-socket
requests in FIFO order.  Socket requests will not block indefinitely
permitting timely cancellation of all requests.

Due to the now-tight coupling of the AIO subsystem with file types,
the AIO subsystem is now a standard part of all kernels.  The VFS_AIO
kernel option and aio.ko module are gone.

Many file types may block indefinitely in their fo_read or fo_write
callbacks resulting in a hung AIO daemon.  This can result in hung
user processes (when processes attempt to cancel all outstanding
requests during exit) or a hung system.  To protect against this, AIO
requests are only permitted for known "safe" files by default.  AIO
requests for all file types can be enabled by setting the new
vfs.aio.enable_usafe sysctl to a non-zero value.  The AIO tests have
been updated to skip operations on unsafe file types if the sysctl is
zero.

Currently, AIO requests on sockets and raw disks are considered safe
and are enabled by default.  aio_mlock() is also enabled by default.

Reviewed by:	cem, jilles
Discussed with:	kib (earlier version)
Sponsored by:	Chelsio Communications
Differential Revision:	https://reviews.freebsd.org/D5289

1 files changed, 4 insertions, 0 deletions

diff --git a/sys/sys/sockbuf.h b/sys/sys/sockbuf.h
index 6631593..c0148b4 100644
--- a/sys/sys/sockbuf.h
+++ b/sys/sys/sockbuf.h
@@ -36,6 +36,7 @@
 #include <sys/_lock.h>
 #include <sys/_mutex.h>
 #include <sys/_sx.h>
+#include <sys/_task.h>
 
 #define	SB_MAX		(2*1024*1024)	/* default for max chars in sockbuf */
 
@@ -53,6 +54,7 @@
 #define	SB_IN_TOE	0x400		/* socket buffer is in the middle of an operation */
 #define	SB_AUTOSIZE	0x800		/* automatically size socket buffer */
 #define	SB_STOP		0x1000		/* backpressure indicator */
+#define	SB_AIO_RUNNING	0x2000		/* AIO operation running */
 
 #define	SBS_CANTSENDMORE	0x0010	/* can't send more data to peer */
 #define	SBS_CANTRCVMORE		0x0020	/* can't receive more data from peer */
@@ -107,6 +109,8 @@ struct	sockbuf {
 	short	sb_flags;	/* (a) flags, see below */
 	int	(*sb_upcall)(struct socket *, void *, int); /* (a) */
 	void	*sb_upcallarg;	/* (a) */
+	TAILQ_HEAD(, kaiocb) sb_aiojobq; /* (a) pending AIO ops */
+	struct	task sb_aiotask; /* AIO task */
 };
 
 #ifdef _KERNEL