add discard option -d to swapon

Signed-off-by: Matt Whitlock <busybox@mattwhitlock.name>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 85 insertions, 9 deletions

diff --git a/util-linux/Config.src b/util-linux/Config.src
index 5a8b0063b..c1cd6daa4 100644
--- a/util-linux/Config.src
+++ b/util-linux/Config.src
@@ -599,6 +599,15 @@ config SWAPONOFF
           space. If you are not using any swap space, you can leave this
           option disabled.
 
+config FEATURE_SWAPON_DISCARD
+        bool "Support discard option -d"
+        default y
+        depends on SWAPONOFF
+        help
+          Enable support for discarding swap area blocks at swapon and/or as
+          the kernel frees them. This option enables both the -d option on
+          'swapon' and the 'discard' option for swap entries in /etc/fstab.
+
 config FEATURE_SWAPON_PRI
         bool "Support priority option -p"
         default y
diff --git a/util-linux/swaponoff.c b/util-linux/swaponoff.c
index d5bfe1888..a7ad6db79 100644
--- a/util-linux/swaponoff.c
+++ b/util-linux/swaponoff.c
@@ -8,10 +8,14 @@
  */
 
 //usage:#define swapon_trivial_usage
-//usage:       "[-a]" IF_FEATURE_SWAPON_PRI(" [-p PRI]") " [DEVICE]"
+//usage:       "[-a]" IF_FEATURE_SWAPON_DISCARD(" [-d[POL]]") IF_FEATURE_SWAPON_PRI(" [-p PRI]") " [DEVICE]"
 //usage:#define swapon_full_usage "\n\n"
 //usage:       "Start swapping on DEVICE\n"
 //usage:     "\n        -a      Start swapping on all swap devices"
+//usage:        IF_FEATURE_SWAPON_DISCARD(
+//usage:     "\n        -d[POL] Discard blocks at swapon (POL=once),"
+//usage:     "\n                as freed (POL=pages), or both (POL omitted)"
+//usage:        )
 //usage:        IF_FEATURE_SWAPON_PRI(
 //usage:     "\n        -p PRI  Set swap device priority"
 //usage:        )
@@ -38,7 +42,22 @@
 # define MNTTYPE_SWAP "swap"
 #endif
 
-#if ENABLE_FEATURE_SWAPON_PRI
+#if ENABLE_FEATURE_SWAPON_DISCARD
+#ifndef SWAP_FLAG_DISCARD
+#define SWAP_FLAG_DISCARD 0x10000
+#endif
+#ifndef SWAP_FLAG_DISCARD_ONCE
+#define SWAP_FLAG_DISCARD_ONCE 0x20000
+#endif
+#ifndef SWAP_FLAG_DISCARD_PAGES
+#define SWAP_FLAG_DISCARD_PAGES 0x40000
+#endif
+#define SWAP_FLAG_DISCARD_MASK \
+        (SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_ONCE | SWAP_FLAG_DISCARD_PAGES)
+#endif
+
+
+#if ENABLE_FEATURE_SWAPON_DISCARD || ENABLE_FEATURE_SWAPON_PRI
 struct globals {
         int flags;
 } FIX_ALIASING;
@@ -98,9 +117,23 @@ static int do_em_all(void)
                         if (applet_name[5] != 'n'
                          || hasmntopt(m, MNTOPT_NOAUTO) == NULL
                         ) {
-#if ENABLE_FEATURE_SWAPON_PRI
+#if ENABLE_FEATURE_SWAPON_DISCARD || ENABLE_FEATURE_SWAPON_PRI
                                 char *p;
                                 g_flags = cl_flags; /* each swap space might have different flags */
+#if ENABLE_FEATURE_SWAPON_DISCARD
+                                p = hasmntopt(m, "discard");
+                                if (p) {
+                                        if (p[7] == '=') {
+                                                if (strncmp(p + 8, "once", 4) == 0 && (p[12] == ',' || p[12] == '\0'))
+                                                        g_flags = (g_flags & ~SWAP_FLAG_DISCARD_MASK) | SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_ONCE;
+                                                else if (strncmp(p + 8, "pages", 5) == 0 && (p[13] == ',' || p[13] == '\0'))
+                                                        g_flags = (g_flags & ~SWAP_FLAG_DISCARD_MASK) | SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_PAGES;
+                                        }
+                                        else if (p[7] == ',' || p[7] == '\0')
+                                                g_flags = (g_flags & ~SWAP_FLAG_DISCARD_MASK) | SWAP_FLAG_DISCARD;
+                                }
+#endif
+#if ENABLE_FEATURE_SWAPON_PRI
                                 p = hasmntopt(m, "pri");
                                 if (p) {
                                         /* Max allowed 32767 (== SWAP_FLAG_PRIO_MASK) */
@@ -112,6 +145,7 @@ static int do_em_all(void)
                                         }
                                 }
 #endif
+#endif
                                 err += swap_enable_disable(m->mnt_fsname);
                         }
                 }
@@ -127,24 +161,57 @@ int swap_on_off_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int swap_on_off_main(int argc UNUSED_PARAM, char **argv)
 {
         int ret;
+#if ENABLE_FEATURE_SWAPON_DISCARD
+        char *discard = NULL;
+#endif
 #if ENABLE_FEATURE_SWAPON_PRI
         unsigned prio;
 #endif
 
         INIT_G();
 
-#if !ENABLE_FEATURE_SWAPON_PRI
+#if !ENABLE_FEATURE_SWAPON_DISCARD && !ENABLE_FEATURE_SWAPON_PRI
         ret = getopt32(argv, "a");
 #else
+#if ENABLE_FEATURE_SWAPON_PRI
         if (applet_name[5] == 'n')
                 opt_complementary = "p+";
-        ret = getopt32(argv, (applet_name[5] == 'n') ? "ap:" : "a", &prio);
+#endif
+        ret = getopt32(argv, (applet_name[5] == 'n') ?
+#if ENABLE_FEATURE_SWAPON_DISCARD
+                "d::"
+#endif
+#if ENABLE_FEATURE_SWAPON_PRI
+                "p:"
+#endif
+                "a" : "a"
+#if ENABLE_FEATURE_SWAPON_DISCARD
+                , &discard
+#endif
+#if ENABLE_FEATURE_SWAPON_PRI
+                , &prio
+#endif
+                );
+#endif
 
-        if (ret & 2) { // -p
-                g_flags = SWAP_FLAG_PREFER |
-                        MIN(prio, SWAP_FLAG_PRIO_MASK);
-                ret &= 1;
+#if ENABLE_FEATURE_SWAPON_DISCARD
+        if (ret & 1) { // -d
+                if (!discard)
+                        g_flags |= SWAP_FLAG_DISCARD;
+                else if (strcmp(discard, "once") == 0)
+                        g_flags |= SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_ONCE;
+                else if (strcmp(discard, "pages") == 0)
+                        g_flags |= SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_PAGES;
+                else
+                        bb_show_usage();
         }
+        ret >>= 1;
+#endif
+#if ENABLE_FEATURE_SWAPON_PRI
+        if (ret & 1) // -p
+                g_flags |= SWAP_FLAG_PREFER |
+                        MIN(prio, SWAP_FLAG_PRIO_MASK);
+        ret >>= 1;
 #endif
 
         if (ret /* & 1: not needed */) // -a