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diff --git a/lib/libc/sys/swapon.2 b/lib/libc/sys/swapon.2
--- a/lib/libc/sys/swapon.2
+++ b/lib/libc/sys/swapon.2
@@ -28,7 +28,7 @@
.\" @(#)swapon.2 8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
-.Dd March 30, 2020
+.Dd December 2, 2021
.Dt SWAPON 2
.Os
.Sh NAME
@@ -37,6 +37,8 @@
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
+.It vm/vm_param.h
+.It vm/swap_pager.h
.In unistd.h
.Ft int
.Fn swapon "const char *special"
@@ -63,6 +65,39 @@
system call disables paging and swapping on the given device.
All associated swap metadata are deallocated, and the device
is made available for other purposes.
+.Pp
+The
+.Fa special
+argument points to either the string that names the special device
+used for swapping or the following structure
+.Bd -literal
+struct swapoff_new_args {
+ const char *name_old_syscall;
+ const char *name;
+ u_int flags;
+};
+.Ed
+use of which allows to augment the syscall behavior.
+The
+.Va name_old_syscall
+member must be initialized to
+.Dv NULL
+for the system to recognize the extended syscall.
+It is recommended to zero the whole structure for future compatibility,
+due to padding.
+.Pp
+The
+.Va name
+string is the special device name, same as legacy syscall argument.
+.The
+.Va flags
+argument takes the following flags:
+.Bl -tag -width SWAPOFF_FORCE
+.It Dv SWAPOFF_FORCE
+Turns off very conservative heuristic which otherwise prevents swapoff
+if it is possible that total amount of free memory and remaining swap
+devices space is unsufficient for system operations.
+.El
.Sh RETURN VALUES
If an error has occurred, a value of -1 is returned and
.Va errno
diff --git a/sbin/swapon/swapon.8 b/sbin/swapon/swapon.8
--- a/sbin/swapon/swapon.8
+++ b/sbin/swapon/swapon.8
@@ -28,7 +28,7 @@
.\" @(#)swapon.8 8.1 (Berkeley) 6/5/93
.\" $FreeBSD$
.\"
-.Dd May 19, 2020
+.Dd November 29, 2021
.Dt SWAPON 8
.Os
.Sh NAME
@@ -42,9 +42,9 @@
.Nm swapoff
.Oo Fl F Ar fstab
.Oc
-.Fl aLq | Ar
+.Fl afLq | Ar
.Nm swapctl
-.Op Fl AghklmsU
+.Op Fl AfghklmsU
.Oo
.Fl a Ar
|
@@ -125,9 +125,15 @@
written to standard output when a swap device is removed.
Note that
.Nm swapoff
-will fail and refuse to remove a swap device if there is insufficient
+will fail and refuse to remove a swap device if some very conservative
+estimation reports that there is insufficient
VM (memory + remaining swap devices) to run the system.
The
+.Fl f
+option turns off this heuristic, which could deadlock the system
+if there is insufficient swap space remaining.
+.Pp
+The
.Nm swapoff
utility
must move swapped pages out of the device being removed which could
diff --git a/sbin/swapon/swapon.c b/sbin/swapon/swapon.c
--- a/sbin/swapon/swapon.c
+++ b/sbin/swapon/swapon.c
@@ -51,6 +51,7 @@
#include <sys/sysctl.h>
#include <sys/wait.h>
#include <vm/vm_param.h>
+#include <vm/swap_pager.h>
#include <err.h>
#include <errno.h>
@@ -78,7 +79,7 @@
static enum { SWAPON, SWAPOFF, SWAPCTL } orig_prog, which_prog = SWAPCTL;
-static int Eflag, qflag;
+static int Eflag, fflag, qflag;
int
main(int argc, char **argv)
@@ -101,7 +102,7 @@
doall = 0;
etc_fstab = NULL;
- while ((ch = getopt(argc, argv, "AadEghklLmqsUF:")) != -1) {
+ while ((ch = getopt(argc, argv, "AadEfghklLmqsUF:")) != -1) {
switch(ch) {
case 'A':
if (which_prog == SWAPCTL) {
@@ -128,6 +129,12 @@
else
usage();
break;
+ case 'f':
+ if (which_prog == SWAPOFF)
+ fflag = 1;
+ else
+ usage();
+ break;
case 'g':
hflag = 'G';
break;
@@ -782,12 +789,18 @@
static const char *
swap_on_off_sfile(const char *name, int doingall)
{
+ struct swapoff_new_args sa;
int error;
if (which_prog == SWAPON)
error = Eflag ? swapon_trim(name) : swapon(name);
- else /* SWAPOFF */
- error = swapoff(name);
+ else { /* SWAPOFF */
+ bzero(&sa, sizeof(sa));
+ sa.name = name;
+ if (fflag)
+ sa.flags |= SWAPOFF_FORCE;
+ error = swapoff((const char *)&sa);
+ }
if (error == -1) {
switch (errno) {
@@ -820,7 +833,7 @@
fprintf(stderr, "[-F fstab] -aLq | [-E] file ...\n");
break;
case SWAPOFF:
- fprintf(stderr, "[-F fstab] -aLq | file ...\n");
+ fprintf(stderr, "[-F fstab] -afLq | file ...\n");
break;
case SWAPCTL:
fprintf(stderr, "[-AghklmsU] [-a file ... | -d file ...]\n");
diff --git a/sys/vm/swap_pager.h b/sys/vm/swap_pager.h
--- a/sys/vm/swap_pager.h
+++ b/sys/vm/swap_pager.h
@@ -69,6 +69,16 @@
#define SW_UNMAPPED 0x01
#define SW_CLOSING 0x04
+struct swapoff_new_args {
+ const char *name_old_syscall;
+ const char *name;
+ u_int flags;
+ u_int pad0;
+ uintptr_t pad1[8];
+};
+
+#define SWAPOFF_FORCE 0x00000001
+
#ifdef _KERNEL
extern int swap_pager_avail;
diff --git a/sys/vm/swap_pager.c b/sys/vm/swap_pager.c
--- a/sys/vm/swap_pager.c
+++ b/sys/vm/swap_pager.c
@@ -470,7 +470,7 @@
static int swapongeom(struct vnode *);
static int swaponvp(struct thread *, struct vnode *, u_long);
static int swapoff_one(struct swdevt *sp, struct ucred *cred,
- bool ignore_check);
+ u_int flags);
/*
* Swap bitmap functions
@@ -2340,10 +2340,6 @@
};
#endif
-/*
- * MPSAFE
- */
-/* ARGSUSED */
int
sys_swapon(struct thread *td, struct swapon_args *uap)
{
@@ -2489,25 +2485,44 @@
};
#endif
-/*
- * MPSAFE
- */
-/* ARGSUSED */
int
sys_swapoff(struct thread *td, struct swapoff_args *uap)
{
struct vnode *vp;
struct nameidata nd;
struct swdevt *sp;
- int error;
+ struct swapoff_new_args sa;
+ int error, probe_byte;
error = priv_check(td, PRIV_SWAPOFF);
if (error)
return (error);
+ /*
+ * Detect old vs. new-style swapoff(2) syscall. The first
+ * pointer in the memory pointed to by uap->name is NULL for
+ * the new variant.
+ */
+ probe_byte = fubyte(uap->name);
+ switch (probe_byte) {
+ case -1:
+ return (EFAULT);
+ case 0:
+ error = copyin(uap->name, &sa, sizeof(sa));
+ if (error != 0)
+ return (error);
+ if ((sa.flags & ~(SWAPOFF_FORCE)) != 0)
+ return (EINVAL);
+ break;
+ default:
+ bzero(&sa, sizeof(sa));
+ sa.name = uap->name;
+ break;
+ }
+
sx_xlock(&swdev_syscall_lock);
- NDINIT(&nd, LOOKUP, FOLLOW | AUDITVNODE1, UIO_USERSPACE, uap->name);
+ NDINIT(&nd, LOOKUP, FOLLOW | AUDITVNODE1, UIO_USERSPACE, sa.name);
error = namei(&nd);
if (error)
goto done;
@@ -2524,14 +2539,14 @@
error = EINVAL;
goto done;
}
- error = swapoff_one(sp, td->td_ucred, false);
+ error = swapoff_one(sp, td->td_ucred, sa.flags);
done:
sx_xunlock(&swdev_syscall_lock);
return (error);
}
static int
-swapoff_one(struct swdevt *sp, struct ucred *cred, bool ignore_check)
+swapoff_one(struct swdevt *sp, struct ucred *cred, u_int flags)
{
u_long nblks;
#ifdef MAC
@@ -2561,7 +2576,7 @@
* means that we can lose swap data when filesystems go away,
* which is arguably worse.
*/
- if (!ignore_check &&
+ if ((flags & SWAPOFF_FORCE) == 0 &&
vm_free_count() + swap_pager_avail < nblks + nswap_lowat)
return (ENOMEM);
@@ -2612,7 +2627,7 @@
devname = devtoname(sp->sw_vp->v_rdev);
else
devname = "[file]";
- error = swapoff_one(sp, thread0.td_ucred, true);
+ error = swapoff_one(sp, thread0.td_ucred, SWAPOFF_FORCE);
if (error != 0) {
printf("Cannot remove swap device %s (error=%d), "
"skipping.\n", devname, error);

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