[Libguestfs] [PATCH] inspect: try to use /etc/os-release on Linux guests

[Pino Toscano]

If a Linux guest has /etc/os-release (mandatory for systemd, so all the
recent Linux distributions have it), try to parse it for the distro, its
version, and its product name.  If we cannot get all of them, the
detection as done so far continues.

Other than changes in the product_name string (which is free-form
anyway, and already documented to not be parseable), there should be no
regressions in the detected distro and version.
---
 src/inspect-fs-unix.c | 143 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 143 insertions(+)

diff --git a/src/inspect-fs-unix.c b/src/inspect-fs-unix.c
index 65ab8ef..19975a7 100644
--- a/src/inspect-fs-unix.c
+++ b/src/inspect-fs-unix.c
@@ -141,6 +141,140 @@ parse_release_file (guestfs_h *g, struct inspect_fs *fs,
   return 0;
 }
 
+/* Parse a os-release file.
+ *
+ * Only few fields are parsed, falling back to the usual detection if we
+ * cannot read all of them.
+ *
+ * For the format of os-release, see also:
+ * http://www.freedesktop.org/software/systemd/man/os-release.html
+ */
+static int
+parse_os_release (guestfs_h *g, struct inspect_fs *fs, const char *filename)
+{
+  int64_t size;
+  CLEANUP_FREE_STRING_LIST char **lines = NULL;
+  size_t i;
+  enum inspect_os_distro distro = OS_DISTRO_UNKNOWN;
+  CLEANUP_FREE char *product_name = NULL;
+  int major_version = -1, minor_version = -1;
+
+  /* Don't trust guestfs_read_lines not to break with very large files.
+   * Check the file size is something reasonable first.
+   */
+  size = guestfs_filesize (g, filename);
+  if (size == -1)
+    /* guestfs_filesize failed and has already set error in handle */
+    return -1;
+  if (size > MAX_SMALL_FILE_SIZE) {
+    error (g, _("size of %s is unreasonably large (%" PRIi64 " bytes)"),
+           filename, size);
+    return -1;
+  }
+
+  lines = guestfs_read_lines (g, filename);
+  if (lines == NULL)
+    return -1;
+
+  for (i = 0; lines[i] != NULL; ++i) {
+    const char *line = lines[i];
+    const char *value;
+    size_t value_len;
+
+    if (line[0] == '#')
+      continue;
+
+    value = strchr (line, '=');
+    if (value == NULL)
+      continue;
+
+    ++value;
+    value_len = strlen (line) - (value - line);
+    if (value_len > 1 && value[0] == '"' && value[value_len-1] == '"') {
+      ++value;
+      value_len -= 2;
+    }
+
+#define VALUE_IS(a) STREQLEN(value, a, value_len)
+    if (STRPREFIX (line, "ID=")) {
+      if (VALUE_IS ("alpine"))
+        distro = OS_DISTRO_ALPINE_LINUX;
+      else if (VALUE_IS ("altlinux"))
+        distro = OS_DISTRO_ALTLINUX;
+      else if (VALUE_IS ("arch"))
+        distro = OS_DISTRO_ARCHLINUX;
+      else if (VALUE_IS ("centos"))
+        distro = OS_DISTRO_CENTOS;
+      else if (VALUE_IS ("debian"))
+        distro = OS_DISTRO_DEBIAN;
+      else if (VALUE_IS ("fedora"))
+        distro = OS_DISTRO_FEDORA;
+      else if (VALUE_IS ("frugalware"))
+        distro = OS_DISTRO_FRUGALWARE;
+      else if (VALUE_IS ("mageia"))
+        distro = OS_DISTRO_MAGEIA;
+      else if (VALUE_IS ("opensuse"))
+        distro = OS_DISTRO_OPENSUSE;
+      else if (VALUE_IS ("rhel"))
+        distro = OS_DISTRO_RHEL;
+      else if (VALUE_IS ("ubuntu"))
+        distro = OS_DISTRO_UBUNTU;
+    } else if (STRPREFIX (line, "PRETTY_NAME=")) {
+      free (product_name);
+      product_name = safe_strndup (g, value, value_len);
+    } else if (STRPREFIX (line, "VERSION_ID=")) {
+      char *major, *minor;
+      if (match2 (g, value, re_major_minor, &major, &minor)) {
+        major_version = guestfs_int_parse_unsigned_int (g, major);
+        free (major);
+        if (major_version == -1) {
+          free (minor);
+          return -1;
+        }
+        minor_version = guestfs_int_parse_unsigned_int (g, minor);
+        free (minor);
+        if (minor_version == -1)
+          return -1;
+      } else {
+        char buf[value_len + 1];
+        snprintf (buf, sizeof buf, "%*s", (int) value_len, value);
+        major_version = guestfs_int_parse_unsigned_int (g, buf);
+        free (major);
+        /* Handle cases where VERSION_ID is not a number. */
+        if (major_version != -1)
+          minor_version = 0;
+      }
+    }
+#undef VALUE_IS
+  }
+
+  /* If we haven't got all the fields, exit right away. */
+  if (distro == OS_DISTRO_UNKNOWN || product_name == NULL ||
+      major_version == -1 || minor_version == -1)
+    return 0;
+
+  /* Apparently, os-release in Debian and CentOS does not provide the full
+   * version number in VERSION_ID, but just the "major" part of it.
+   * Hence, if minor_version is 0, act as there was no information in
+   * os-release, which will continue the inspection using the release files
+   * as done previously.
+   */
+  if ((distro == OS_DISTRO_DEBIAN || distro == OS_DISTRO_CENTOS) &&
+      minor_version == 0)
+    return 0;
+
+  /* We got everything, so set the fields and report the inspection
+   * was successful.
+   */
+  fs->distro = distro;
+  fs->product_name = product_name;
+  product_name = NULL;
+  fs->major_version = major_version;
+  fs->minor_version = minor_version;
+
+  return 1;
+}
+
 /* Ubuntu has /etc/lsb-release containing:
  *   DISTRIB_ID=Ubuntu                                # Distro
  *   DISTRIB_RELEASE=10.04                            # Version
@@ -348,6 +482,15 @@ guestfs_int_check_linux_root (guestfs_h *g, struct inspect_fs *fs)
 
   fs->type = OS_TYPE_LINUX;
 
+  if (guestfs_is_file_opts (g, "/etc/os-release",
+                            GUESTFS_IS_FILE_OPTS_FOLLOWSYMLINKS, 1, -1) > 0) {
+    r = parse_os_release (g, fs, "/etc/os-release");
+    if (r == -1)        /* error */
+      return -1;
+    if (r == 1)         /* ok - detected the release from this file */
+      goto skip_release_checks;
+  }
+
   if (guestfs_is_file_opts (g, "/etc/lsb-release",
                             GUESTFS_IS_FILE_OPTS_FOLLOWSYMLINKS, 1, -1) > 0) {
     r = parse_lsb_release (g, fs, "/etc/lsb-release");
-- 
2.1.0