Allow symlinks to be used in vold managed fstab entrieslinaro-master

Allow symlinks to be used in vold managed fstab entries

With device-tree kernels the sysfs path for SD cards varies depending on
device-tree layout and the actual card used. It is therefore impossible
to specify the sysfs path for the device in fstab.

However, there exists a symlink to the device which is created under a
generic path like '/sys/block/mmcblk0/device'. To use such a path with
vold we need to convert the symlinked path to the real path, which this
patch does.

Change-Id: I68e693772e70b758dab22fcd5f0eb4b9e84a2443
Signed-off-by: Jon Medhurst <tixy@linaro.org>

1 files changed, 18 insertions, 1 deletions

diff --git a/main.cpp b/main.cpp
index d4b7d28d..a2837222 100644
--- a/main.cpp
+++ b/main.cpp
@@ -188,7 +188,24 @@ static int process_config(VolumeManager *vm)
             }
             dv = new DirectVolume(vm, &(fstab->recs[i]), flags);
 
-            if (dv->addPath(fstab->recs[i].blk_device)) {
+            /* To allow symlinked paths to be specified we need to convert
+             * them with realpath(). This is made a bit more complicated
+             * because our paths are relative to the sysfs base, so we need
+             * to prefix them with '/sys' before conversion and also remove
+             * '/sys' from the result (by skipping the first 4 characters).
+             */
+            char* sp = (char*)malloc(4 + strlen(fstab->recs[i].blk_device) + 1);
+            int error = !sp;
+            if (!error) {
+                strcpy(sp, "/sys");
+                strcat(sp, fstab->recs[i].blk_device);
+                char *rp = realpath(sp, NULL);
+                if (rp && strncmp(rp, "/sys", 4)==0)
+                    error = dv->addPath(rp + 4); /* Real path without '/sys' */
+                free(rp);
+                free(sp);
+            }
+            if (error) {
                 SLOGE("Failed to add devpath %s to volume %s",
                       fstab->recs[i].blk_device, fstab->recs[i].label);
                 goto out_fail;