libcutils: add fs_config_generate

Bug: 19908228
Change-Id: Icb0e189a86758bb779b9bdf7c0d92216d297869f

1 files changed, 21 insertions, 0 deletions

diff --git a/libcutils/fs_config.c b/libcutils/fs_config.c
index bdb24dc..7fd66cd 100644
--- a/libcutils/fs_config.c
+++ b/libcutils/fs_config.c
@@ -63,6 +63,8 @@ static inline uint64_t get8LE(const uint8_t* src)
     return ((uint64_t) high << 32) | (uint64_t) low;
 }
 
+#define ALIGN(x, alignment) ( ((x) + ((alignment) - 1)) & ~((alignment) - 1) )
+
 /* Rules for directories.
 ** These rules are applied based on "first match", so they
 ** should start with the most specific path and work their
@@ -261,3 +263,22 @@ void fs_config(const char *path, int dir,
     *mode = (*mode & (~07777)) | pc->mode;
     *capabilities = pc->capabilities;
 }
+
+ssize_t fs_config_generate(char *buffer, size_t length, const struct fs_path_config *pc)
+{
+    struct fs_path_config_from_file *p = (struct fs_path_config_from_file *)buffer;
+    size_t len = ALIGN(sizeof(*p) + strlen(pc->prefix) + 1, sizeof(uint64_t));
+
+    if ((length < len) || (len > UINT16_MAX)) {
+        return -ENOSPC;
+    }
+    memset(p, 0, len);
+    uint16_t host_len = len;
+    p->len = get2LE((const uint8_t *)&host_len);
+    p->mode = get2LE((const uint8_t *)&(pc->mode));
+    p->uid = get2LE((const uint8_t *)&(pc->uid));
+    p->gid = get2LE((const uint8_t *)&(pc->gid));
+    p->capabilities = get8LE((const uint8_t *)&(pc->capabilities));
+    strcpy(p->prefix, pc->prefix);
+    return len;
+}