util: add an API to retrieve the resolved path to a virCommand's binary

The binary to be exec'ed by virExec() is stored in
virCommand::args[0], and is resolved to a full absolute path (stored
in a local of virExec() just prior to execve().

Since we will have another use for the full absolute path, lets make
an API to resolve/retrieve the absolute path, and cache it in
virCommand::binaryPath so we only have to do the resolution once.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/libvirt_private.syms

@@ -2091,6 +2091,7 @@ virCommandDryRunTokenNew;
 virCommandExec;
 virCommandFree;
 virCommandGetArgList;
+virCommandGetBinaryPath;
 virCommandGetGID;
 virCommandGetUID;
 virCommandHandshakeNotify;

src/util/vircommand.c

@@ -88,6 +88,7 @@ struct _virCommandSendBuffer {
 struct _virCommand {
     int has_error; /* 0 on success, -1 on error  */
 
+    char *binaryPath; /* only valid if args[0] isn't absolute path */
     char **args;
     size_t nargs;
     size_t maxargs;
@@ -630,6 +631,7 @@ virCommandMassClose(virCommand *cmd,
 
 # endif /* ! __FreeBSD__ */
 
+
 /*
  * virExec:
  * @cmd virCommand * containing all information about the program to
@@ -646,22 +648,13 @@ virExec(virCommand *cmd)
     int childin = cmd->infd;
     int childout = -1;
     int childerr = -1;
-    g_autofree char *binarystr = NULL;
     const char *binary = NULL;
     int ret;
     g_autofree gid_t *groups = NULL;
     int ngroups;
 
-    if (!g_path_is_absolute(cmd->args[0])) {
+    if (!(binary = virCommandGetBinaryPath(cmd)))
-        if (!(binary = binarystr = virFindFileInPath(cmd->args[0]))) {
+        return -1;
-            virReportSystemError(ENOENT,
-                                 _("Cannot find '%s' in path"),
-                                 cmd->args[0]);
-            return -1;
-        }
-    } else {
-        binary = cmd->args[0];
-    }
 
     if (childin < 0) {
         if (getDevNull(&null) < 0)
@@ -2164,6 +2157,40 @@ virCommandGetArgList(virCommand *cmd,
 }
 
 
+/*
+ * virCommandGetBinaryPath:
+ * @cmd: virCommand* containing all information about the program
+ *
+ * If args[0] is an absolute path, return that. If not, then resolve
+ * args[0] to a full absolute path, cache that in binaryPath, and
+ * return a pointer to this resolved string. binaryPath is only set by
+ * calling this function, so even other virCommand functions should
+ * access binaryPath via this function.
+ *
+ * returns const char* with the full path of the binary to be
+ * executed, or NULL on failure.
+ */
+const char *
+virCommandGetBinaryPath(virCommand *cmd)
+{
+
+    if (cmd->binaryPath)
+        return cmd->binaryPath;
+
+    if (g_path_is_absolute(cmd->args[0]))
+        return cmd->args[0];
+
+    if (!(cmd->binaryPath = virFindFileInPath(cmd->args[0]))) {
+        virReportSystemError(ENOENT,
+                             _("Cannot find '%s' in path"),
+                             cmd->args[0]);
+        return NULL;
+    }
+
+    return cmd->binaryPath;
+}
+
+
 #ifndef WIN32
 /*
  * Manage input and output to the child process.
@@ -3015,6 +3042,8 @@ virCommandFree(virCommand *cmd)
     VIR_FORCE_CLOSE(cmd->outfd);
     VIR_FORCE_CLOSE(cmd->errfd);
 
+    g_free(cmd->binaryPath);
+
     for (i = 0; i < cmd->nargs; i++)
         g_free(cmd->args[i]);
     g_free(cmd->args);

src/util/vircommand.h

@@ -170,6 +170,7 @@ int virCommandToStringBuf(virCommand *cmd,
                           bool linebreaks,
                           bool stripCommandPath);
 
+const char *virCommandGetBinaryPath(virCommand *cmd);
 int virCommandGetArgList(virCommand *cmd, char ***args);
 
 int virCommandExec(virCommand *cmd, gid_t *groups, int ngroups) G_GNUC_WARN_UNUSED_RESULT;