mount: shared-subtree support

This patch builds shared-subtree semantics awareness into the mount
command.  Updates the man page for mount too.

The patch also fix a conflict between MS_COMMENT and MS_UNBINDABLE
(-- kzak).

Signed-off-by: Karel Zak <kzak@redhat.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>

diff --git a/mount/mount.8 b/mount/mount.8
index 2cfaae243b8185fe01fa715672658e68913f496e..870cfd13e7b46a641520062cf70214c879603348 100644 (file)
--- a/mount/mount.8
+++ b/mount/mount.8
@@ -131,6 +131,41 @@ to another place. The call is
 .B "mount --move olddir newdir"
 .RE
 
+Since Linux 2.6.15 it is possible to mark a mount and its submounts as shared,
+private, slave or unbindable. A shared mount provides ability to create mirrors
+of that mount such that mounts and umounts within any of the mirrors propagate
+to the other mirror. A slave mount receives propagation from its master, but
+any not vice-versa.  A private mount carries no propagation abilities.  A
+unbindable mount is a private mount which cannot cloned through a bind
+operation. Detailed semantics is documented in Documentation/sharedsubtree.txt
+file in the kernel source tree.
+.RS
+.br
+.B "mount --make-shared mountpoint"
+.br
+.B "mount --make-slave mountpoint"
+.br
+.B "mount --make-private mountpoint"
+.br
+.B "mount --make-unbindable mountpoint"
+.br
+.RE
+
+The following commands allows one to recursively change the type of all the
+mounts under a given mountpoint.
+.RS
+.br
+.B "mount --make-rshared mountpoint"
+.br
+.B "mount --make-rslave mountpoint"
+.br
+.B "mount --make-rprivate mountpoint"
+.br
+.B
+"mount --make-runbindable mountpoint"
+.br
+.RE
+
 The
 .I proc
 file system is not associated with a special device, and when

diff --git a/mount/mount.c b/mount/mount.c
index 6c9aec077896e912724832d323b1dce649c1eba5..1d179b72a23c4f93ec0bcb17cb7cc89b06da8534 100644 (file)
--- a/mount/mount.c
+++ b/mount/mount.c
@@ -84,7 +84,9 @@ static int optfork = 0;
 /* Add volumelabel in a listing of mounted devices (-l). */
 static int list_with_volumelabel = 0;
 
-/* Nonzero for mount {--bind|--replace|--before|--after|--over|--move} */
+/* Nonzero for mount {--bind|--replace|--before|--after|--over|--move|
+ *                    make-shared|make-private|make-unbindable|make-slave}
+ */
 static int mounttype = 0;
 
 /* True if ruid != euid.  */
@@ -108,7 +110,7 @@ struct opt_map {
 #define MS_USER                0x20000000
 #define MS_OWNER       0x10000000
 #define MS_GROUP       0x08000000
-#define MS_COMMENT     0x00020000
+#define MS_COMMENT     0x02000000
 #define MS_LOOP                0x00010000
 
 /* Options that we keep the mount system call from seeing.  */
@@ -117,6 +119,8 @@ struct opt_map {
 /* Options that we keep from appearing in the options field in the mtab.  */
 #define MS_NOMTAB      (MS_REMOUNT|MS_NOAUTO|MS_USERS|MS_USER)
 
+#define MS_PROPAGATION  (MS_SHARED|MS_SLAVE|MS_UNBINDABLE|MS_PRIVATE)
+
 /* Options that we make ordinary users have by default.  */
 #define MS_SECURE      (MS_NOEXEC|MS_NOSUID|MS_NODEV)
 
@@ -349,6 +353,9 @@ parse_opts (const char *options, int *flags, char **extra_opts) {
                *flags |= MS_RDONLY;
        if (readwrite)
                *flags &= ~MS_RDONLY;
+
+       if (mounttype & MS_PROPAGATION)
+               *flags &= ~MS_BIND;
        *flags |= mounttype;
 }
 
@@ -901,13 +908,15 @@ retry_nfs:
       if (loop)
          opt_loopdev = loopdev;
 
-      update_mtab_entry(loop ? loopfile : spec,
+      if (!(mounttype & MS_PROPAGATION)) {
+             update_mtab_entry(loop ? loopfile : spec,
                        node,
                        types ? types : "unknown",
                        fix_opts_string (flags & ~MS_NOMTAB, extra_opts, user),
                        flags,
                        freq,
                        pass);
+      }
 
       block_signals (SIG_UNBLOCK);
       res = 0;
@@ -1447,6 +1456,14 @@ static struct option longopts[] = {
        { "move", 0, 0, 133 },
        { "guess-fstype", 1, 0, 134 },
        { "rbind", 0, 0, 135 },
+       { "make-shared", 0, 0, 136 },
+       { "make-slave", 0, 0, 137 },
+       { "make-private", 0, 0, 138 },
+       { "make-unbindable", 0, 0, 139 },
+       { "make-rshared", 0, 0, 140 },
+       { "make-rslave", 0, 0, 141 },
+       { "make-rprivate", 0, 0, 142 },
+       { "make-runbindable", 0, 0, 143 },
        { "internal-only", 0, 0, 'i' },
        { NULL, 0, 0, 0 }
 };
@@ -1473,6 +1490,17 @@ usage (FILE *fp, int n) {
          "       mount --bind olddir newdir\n"
          "or move a subtree:\n"
          "       mount --move olddir newdir\n"
+         "One can change the type of mount containing the directory dir:\n"
+         "       mount --make-shared dir\n"
+         "       mount --make-slave dir\n"
+         "       mount --make-private dir\n"
+         "       mount --make-unbindable dir\n"
+         "One can change the type of all the mounts in a mount subtree\n"
+         "containing the directory dir:\n"
+         "       mount --make-rshared dir\n"
+         "       mount --make-rslave dir\n"
+         "       mount --make-rprivate dir\n"
+         "       mount --make-runbindable dir\n"
          "A device can be given by name, say /dev/hda1 or /dev/cdrom,\n"
          "or by label, using  -L label  or by uuid, using  -U uuid .\n"
          "Other options: [-nfFrsvw] [-o options] [-p passwdfd].\n"
@@ -1627,6 +1655,39 @@ main(int argc, char *argv[]) {
                case 135:
                        mounttype = (MS_BIND | MS_REC);
                        break;
+
+               case 136:
+                       mounttype = MS_SHARED;
+                       break;
+
+               case 137:
+                       mounttype = MS_SLAVE;
+                       break;
+
+               case 138:
+                       mounttype = MS_PRIVATE;
+                       break;
+
+               case 139:
+                       mounttype = MS_UNBINDABLE;
+                       break;
+
+               case 140:
+                       mounttype = (MS_SHARED | MS_REC);
+                       break;
+
+               case 141:
+                       mounttype = (MS_SLAVE | MS_REC);
+                       break;
+
+               case 142:
+                       mounttype = (MS_PRIVATE | MS_REC);
+                       break;
+
+               case 143:
+                       mounttype = (MS_UNBINDABLE | MS_REC);
+                       break;
+
                case '?':
                default:
                        usage (stderr, EX_USAGE);

diff --git a/mount/mount_constants.h b/mount/mount_constants.h
index 61e89697f6fd4642b921b3beb06a4c78df3510f6..5c3897f81165eec9e82ddc59c091b5894490f6f8 100644 (file)
--- a/mount/mount_constants.h
+++ b/mount/mount_constants.h
@@ -57,6 +57,18 @@ if we have a stack or plain mount - mount atop of it, forming a stack. */
 #ifndef MS_VERBOSE
 #define MS_VERBOSE     0x8000  /* 32768 */
 #endif
+#ifndef MS_UNBINDABLE
+#define MS_UNBINDABLE  (1<<17) /* 131072 unbindable*/
+#endif
+#ifndef MS_PRIVATE
+#define MS_PRIVATE     (1<<18) /* 262144 Private*/
+#endif
+#ifndef MS_SLAVE
+#define MS_SLAVE       (1<<19) /* 524288 Slave*/
+#endif
+#ifndef MS_SHARED
+#define MS_SHARED      (1<<20) /* 1048576 Shared*/
+#endif
 /*
  * Magic mount flag number. Had to be or-ed to the flag values.
  */