Add functions for checking if user or group exists

Instead of duplicating the code from virGet{User,Group}IDByName(), which are
static anyway, extend those functions to accept NULL pointers for the result and
a boolean for controlling the error reporting.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

src/libvirt_private.syms

@@ -3090,6 +3090,8 @@ virUSBDeviceSetUsedBy;
 
 
 # util/virutil.h
+virDoesGroupExist;
+virDoesUserExist;
 virDoubleToStr;
 virEnumFromString;
 virEnumToString;

src/util/virutil.c

@@ -971,9 +971,11 @@ char *virGetGroupName(gid_t gid)
 
 /* Search in the password database for a user id that matches the user name
  * `name`. Returns 0 on success, -1 on failure or 1 if name cannot be found.
+ *
+ * Warns if @missing_ok is false
  */
 static int
-virGetUserIDByName(const char *name, uid_t *uid)
+virGetUserIDByName(const char *name, uid_t *uid, bool missing_ok)
 {
     char *strbuf = NULL;
     struct passwd pwbuf;
@@ -996,7 +998,7 @@ virGetUserIDByName(const char *name, uid_t *uid)
     }
 
     if (!pw) {
-        if (rc != 0) {
+        if (rc != 0 && !missing_ok) {
             char buf[1024];
             /* log the possible error from getpwnam_r. Unfortunately error
              * reporting from this function is bad and we can't really
@@ -1009,7 +1011,8 @@ virGetUserIDByName(const char *name, uid_t *uid)
         goto cleanup;
     }
 
-    *uid = pw->pw_uid;
+    if (uid)
+        *uid = pw->pw_uid;
     ret = 0;
 
  cleanup:
@@ -1032,7 +1035,7 @@ virGetUserID(const char *user, uid_t *uid)
     if (*user == '+') {
         user++;
     } else {
-        int rc = virGetUserIDByName(user, uid);
+        int rc = virGetUserIDByName(user, uid, false);
         if (rc <= 0)
             return rc;
     }
@@ -1051,9 +1054,11 @@ virGetUserID(const char *user, uid_t *uid)
 
 /* Search in the group database for a group id that matches the group name
  * `name`. Returns 0 on success, -1 on failure or 1 if name cannot be found.
+ *
+ * Warns if @missing_ok is false
  */
 static int
-virGetGroupIDByName(const char *name, gid_t *gid)
+virGetGroupIDByName(const char *name, gid_t *gid, bool missing_ok)
 {
     char *strbuf = NULL;
     struct group grbuf;
@@ -1076,7 +1081,7 @@ virGetGroupIDByName(const char *name, gid_t *gid)
     }
 
     if (!gr) {
-        if (rc != 0) {
+        if (rc != 0 && !missing_ok) {
             char buf[1024];
             /* log the possible error from getgrnam_r. Unfortunately error
              * reporting from this function is bad and we can't really
@@ -1089,7 +1094,8 @@ virGetGroupIDByName(const char *name, gid_t *gid)
         goto cleanup;
     }
 
-    *gid = gr->gr_gid;
+    if (gid)
+        *gid = gr->gr_gid;
     ret = 0;
 
  cleanup:
@@ -1112,7 +1118,7 @@ virGetGroupID(const char *group, gid_t *gid)
     if (*group == '+') {
         group++;
     } else {
-        int rc = virGetGroupIDByName(group, gid);
+        int rc = virGetGroupIDByName(group, gid, false);
         if (rc <= 0)
             return rc;
     }
@@ -1129,6 +1135,24 @@ virGetGroupID(const char *group, gid_t *gid)
     return 0;
 }
 
+/* Silently checks if User @name exists.
+ * Returns if the user exists and fallbacks to false on error.
+ */
+int
+virDoesUserExist(const char *name)
+{
+    return virGetUserIDByName(name, NULL, true) == 0;
+}
+
+/* Silently checks if Group @name exists.
+ * Returns if the group exists and fallbacks to false on error.
+ */
+int
+virDoesGroupExist(const char *name)
+{
+    return virGetGroupIDByName(name, NULL, true) == 0;
+}
+
 
 /* Compute the list of primary and supplementary groups associated
  * with @uid, and including @gid in the list (unless it is -1),

src/util/virutil.h

@@ -152,6 +152,10 @@ int virGetUserID(const char *name,
 int virGetGroupID(const char *name,
                   gid_t *gid) ATTRIBUTE_RETURN_CHECK;
 
+int virDoesUserExist(const char *name);
+int virDoesGroupExist(const char *name);
+
+
 bool virIsDevMapperDevice(const char *dev_name) ATTRIBUTE_NONNULL(1);
 
 bool virValidateWWN(const char *wwn);