Vold: support stacking of storage mounts.

Any stacked mounts must appear in vold.fstab with deepest mount
points listed last. When mounting a volume, vold will scan for mounts
that prefix the desired mount point, and attempt to mount them first.
When unmounting a volume, it will scan for other volumes to which the
current mount point is a prefix, and unmount them first. System is
also permitted to browse (but not read/write) storage mount points,
as otherwise Settings->Storage can not report free/used space due to
access failure.

Change-Id: Id3fd8f9bab5d31084da0c82a478cf9c3bcd6eda3

Author: Unhelpful

Volume.cpp

@@ -19,6 +19,7 @@
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <unistd.h>
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -339,13 +340,41 @@ int Volume::mountVol() {
             return -1;
         }
 
+        if (access(getMountpoint(), F_OK)) {
+            char *myMountpoint = strdup(getMountpoint());
+            if (!myMountpoint) {
+                SLOGE("Allocation failure while mounting %s", devicePath);
+                return -1;
+            }
+            if (*myMountpoint) {
+                if (mDebug) SLOGD("Mount point prepare for \"%s\"", myMountpoint);
+                char *slash = myMountpoint;
+                while (slash) {
+                    slash = strchr(slash + 1, '/');
+                    if (slash)
+                        *slash = 0;
+                    if (mDebug) SLOGD("Check existence of %s", myMountpoint);
+                    if (access(myMountpoint, F_OK)) {
+                        if (mDebug) SLOGD("Create %s", myMountpoint);
+                        if (mkdir(myMountpoint, 0555)) {
+                            SLOGE("Failed to create %s", myMountpoint);
+                            return -1;
+                        }
+                    }
+                    if (slash)
+                        *slash = '/';
+                }
+            }
+            free (myMountpoint);
+        }
+
         /*
          * Mount the device on our internal staging mountpoint so we can
          * muck with it before exposing it to non priviledged users.
          */
         errno = 0;
         if (Fat::doMount(devicePath, "/mnt/secure/staging", false, false, false,
-                1000, 1015, 0702, true)) {
+                1000, 1015, 0602, true)) {
             SLOGE("%s failed to mount (%s)\n", devicePath, strerror(errno));
             continue;
         }

Volume.h

@@ -18,6 +18,7 @@
 #define _VOLUME_H
 
 #include <utils/List.h>
+#include <string.h>
 
 class NetlinkEvent;
 class VolumeManager;
@@ -68,6 +69,13 @@ class Volume {
 
     const char *getLabel() { return mLabel; }
     const char *getMountpoint() { return mMountpoint; }
+    bool isPrefixOf(Volume *v) {
+        const char *myMountpoint = getMountpoint();
+        const char *oMountpoint = v->getMountpoint();
+        int myLen = strlen(myMountpoint);
+        return !strncmp(myMountpoint, oMountpoint, myLen) && (myMountpoint[myLen-1] == '/' || oMountpoint[myLen] == '/');
+    }
+
     int getState() { return mState; }
 
     virtual int handleBlockEvent(NetlinkEvent *evt);

VolumeManager.cpp

@@ -948,12 +948,28 @@ int VolumeManager::mountObb(const char *img, const char *key, int ownerUid) {
 
 int VolumeManager::mountVolume(const char *label) {
     Volume *v = lookupVolume(label);
+    VolumeCollection::iterator it;
 
     if (!v) {
         errno = ENOENT;
         return -1;
     }
 
+    if (mDebug) SLOGD("Mounting %s", v->getMountpoint());
+    for (it = mVolumes->begin(); it != mVolumes->end(); ++it) {
+
+        Volume *cur = *it;
+        const char *mountpoint = cur->getMountpoint();
+        if (mDebug) SLOGD("checking mountpoint %s", mountpoint);
+        if (!strcmp(v->getMountpoint(), mountpoint)) continue;
+        if (cur->isPrefixOf(v) && cur->getState() != Volume::State_Mounted)
+        {
+            int tmp_ret = cur->mountVol();
+            if (tmp_ret < 0)
+                return tmp_ret;
+        }
+    }
+
     return v->mountVol();
 }
 
@@ -1224,6 +1240,7 @@ int VolumeManager::unshareVolume(const char *label, const char *method) {
 
 int VolumeManager::unmountVolume(const char *label, bool force) {
     Volume *v = lookupVolume(label);
+    VolumeCollection::iterator it;
 
     if (!v) {
         errno = ENOENT;
@@ -1242,6 +1259,21 @@ int VolumeManager::unmountVolume(const char *label, bool force) {
         return -1;
     }
 
+    if (mDebug) SLOGD("Unmounting %s", v->getMountpoint());
+    for (it = --(mVolumes->end()); it != mVolumes->end(); it--) {
+        Volume *cur = *it;
+        const char *mountpoint = cur->getMountpoint();
+        if (mDebug) SLOGD("checking mountpoint %s", mountpoint);
+        if (!strcmp(v->getMountpoint(), mountpoint)) continue;
+        if (v->isPrefixOf(cur) && cur->getState() == Volume::State_Mounted)
+        {
+            cleanupAsec(cur, force);
+            int tmp_ret = cur->unmountVol(force);
+            if (tmp_ret < 0)
+                return tmp_ret;
+        }
+    }
+
     cleanupAsec(v, force);
 
     return v->unmountVol(force);