Add SetQuotaInherit API.

This allows setting the "inherit project ID" flags on directories; in
our case, we want to set this on the root of the lower filesystem, eg
"/data/media/0".

Bug: 146419093
Test: manual invocation works
Change-Id: Ic74588fd972d464e7021bef953da0e5aaafc4286
diff --git a/Utils.cpp b/Utils.cpp
index dc1c593..d5e0ca8 100644
--- a/Utils.cpp
+++ b/Utils.cpp
@@ -116,7 +116,33 @@
     }
 }
 
-int SetQuotaProjectId(std::string path, long projectId) {
+int SetQuotaInherit(const std::string& path) {
+    unsigned long flags;
+
+    android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(path.c_str(), O_RDONLY | O_CLOEXEC)));
+    if (fd == -1) {
+        PLOG(ERROR) << "Failed to open " << path << " to set project id inheritance.";
+        return -1;
+    }
+
+    int ret = ioctl(fd, FS_IOC_GETFLAGS, &flags);
+    if (ret == -1) {
+        PLOG(ERROR) << "Failed to get flags for " << path << " to set project id inheritance.";
+        return ret;
+    }
+
+    flags |= FS_PROJINHERIT_FL;
+
+    ret = ioctl(fd, FS_IOC_SETFLAGS, &flags);
+    if (ret == -1) {
+        PLOG(ERROR) << "Failed to set flags for " << path << " to set project id inheritance.";
+        return ret;
+    }
+
+    return 0;
+}
+
+int SetQuotaProjectId(const std::string& path, long projectId) {
     struct fsxattr fsx;
 
     android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(path.c_str(), O_RDONLY | O_CLOEXEC)));