Introduce virFileReadAllQuiet

Just like virFileReadAll, but returns -errno instead
of reporting errors. Useful for ignoring some errors.

src/libvirt_private.syms

@@ -1288,6 +1288,7 @@ virFileOpenAs;
 virFileOpenTty;
 virFilePrintf;
 virFileReadAll;
+virFileReadAllQuiet;
 virFileReadHeaderFD;
 virFileReadLimFD;
 virFileRelLinkPointsTo;

src/util/virfile.c

@@ -1301,6 +1301,21 @@ virFileReadAll(const char *path, int maxlen, char **buf)
     return len;
 }
 
+int
+virFileReadAllQuiet(const char *path, int maxlen, char **buf)
+{
+    int fd = open(path, O_RDONLY);
+    if (fd < 0)
+        return -errno;
+
+    int len = virFileReadLimFD(fd, maxlen, buf);
+    VIR_FORCE_CLOSE(fd);
+    if (len < 0)
+        return -errno;
+
+    return len;
+}
+
 /* Truncate @path and write @str to it.  If @mode is 0, ensure that
    @path exists; otherwise, use @mode if @path must be created.
    Return 0 for success, nonzero for failure.

src/util/virfile.h

@@ -129,6 +129,8 @@ int virFileReadLimFD(int fd, int maxlen, char **buf)
     ATTRIBUTE_RETURN_CHECK ATTRIBUTE_NONNULL(3);
 int virFileReadAll(const char *path, int maxlen, char **buf)
     ATTRIBUTE_RETURN_CHECK ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(3);
+int virFileReadAllQuiet(const char *path, int maxlen, char **buf)
+    ATTRIBUTE_RETURN_CHECK ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(3);
 
 int virFileWriteStr(const char *path, const char *str, mode_t mode)
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_RETURN_CHECK;