switchroot: Replace custom error printing with err/warn functions from libc

The `warn()` libc extension has exactly the same behaviour as our own
`perrorv` function, but is available in (at least) glibc and musl.  As an
added bonus the similar function `err()` which will exit with an error
code afterwards.

This implementation is tidier and allows us to get rid of our own
`perrorv`.  It paves the way to removing `ostree-mount-util.c` to simplify
the build scripts.

Original idea by @cgwalters in #477.

Closes: #478
Approved by: cgwalters

src/switchroot/ostree-mount-util.c

@@ -22,53 +22,19 @@
 
 #include "config.h"
 
-#include <stdarg.h>
+#include <err.h>
-#include <errno.h>
-#include <string.h>
-#include <stdio.h>
-#include <sys/mount.h>
-#include <unistd.h>
 #include <stdlib.h>
 #include <sys/statvfs.h>
 
 #include "ostree-mount-util.h"
 
-int
-perrorv (const char *format, ...)
-{
-  va_list args;
-  char buf[1024];
-  char *p;
-
-#ifdef _GNU_SOURCE
-  p = strerror_r (errno, buf, sizeof (buf));
-#else
-  strerror_r (errno, buf, sizeof (buf));
-  buf[sizeof (buf) - 1] = '\0';
-  p = buf;
-#endif  /* _GNU_SOURCE */
-
-  va_start (args, format);
-
-  vfprintf (stderr, format, args);
-  fprintf (stderr, ": %s\n", p);
-  fflush (stderr);
-
-  va_end (args);
-
-  return 0;
-}
-
 int
 path_is_on_readonly_fs (char *path)
 {
   struct statvfs stvfsbuf;
 
   if (statvfs (path, &stvfsbuf) == -1)
-    {
+    err (EXIT_FAILURE, "statvfs(%s)", path);
-      perrorv ("statvfs(%s): ", path);
-      exit (EXIT_FAILURE);
-    }
 
   return (stvfsbuf.f_flag & ST_RDONLY) != 0;
 }

src/switchroot/ostree-mount-util.h

@@ -21,6 +21,4 @@
 
 #pragma once
 
-int perrorv (const char *format, ...) __attribute__ ((format (printf, 1, 2)));
-
 int path_is_on_readonly_fs (char *path);

src/switchroot/ostree-prepare-root.c

@@ -40,6 +40,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
+#include <err.h>
 #include <errno.h>
 #include <ctype.h>
 
@@ -86,27 +87,18 @@ parse_ostree_cmdline (void)
     {
       // Mount proc
       if (mount ("proc", "/proc", "proc", 0, NULL) < 0)
-        {
+        err (EXIT_FAILURE, "failed to mount proc on /proc");
-          perrorv ("failed to mount proc on /proc: ");
-          exit (EXIT_FAILURE);
-        }
 
       cmdline = read_proc_cmdline ();
       tmp_errno = errno;
 
       /* Leave the filesystem in the state that we found it: */
       if (umount ("/proc"))
-        {
+        err (EXIT_FAILURE, "failed to umount proc from /proc");
-          perrorv ("failed to umount proc from /proc: ");
-          exit (EXIT_FAILURE);
-        }
 
       errno = tmp_errno;
       if (!cmdline)
-        {
+        err (EXIT_FAILURE, "failed to read /proc/cmdline");
-          perrorv ("failed to read /proc/cmdline: ");
-          exit (EXIT_FAILURE);
-        }
     }
 
   iter = cmdline;
@@ -158,29 +150,17 @@ resolve_deploy_path (const char * root_mountpoint)
 
   ostree_target = parse_ostree_cmdline ();
   if (!ostree_target)
-    {
+    errx (EXIT_FAILURE, "No OSTree target; expected ostree=/ostree/boot.N/...");
-      fprintf (stderr, "No OSTree target; expected ostree=/ostree/boot.N/...\n");
-      exit (EXIT_FAILURE);
-    }
 
   snprintf (destpath, sizeof(destpath), "%s/%s", root_mountpoint, ostree_target);
   printf ("Examining %s\n", destpath);
   if (lstat (destpath, &stbuf) < 0)
-    {
+    err (EXIT_FAILURE, "Couldn't find specified OSTree root '%s'", destpath);
-      perrorv ("Couldn't find specified OSTree root '%s': ", destpath);
-      exit (EXIT_FAILURE);
-    }
   if (!S_ISLNK (stbuf.st_mode))
-    {
+    errx (EXIT_FAILURE, "OSTree target is not a symbolic link: %s", destpath);
-      fprintf (stderr, "OSTree target is not a symbolic link: %s\n", destpath);
-      exit (EXIT_FAILURE);
-    }
   deploy_path = realpath (destpath, NULL);
   if (deploy_path == NULL)
-    {
+    err (EXIT_FAILURE, "realpath(%s) failed", destpath);
-      perrorv ("realpath(%s) failed: ", destpath);
-      exit (EXIT_FAILURE);
-    }
   printf ("Resolved OSTree target to: %s\n", deploy_path);
   return deploy_path;
 }
@@ -214,33 +194,21 @@ main(int argc, char *argv[])
    *
    * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
   if (mount (NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
-    {
+    err (EXIT_FAILURE, "failed to make \"/\" private mount");
-      perrorv ("failed to make \"/\" private mount: %m");
-      exit (EXIT_FAILURE);
-    }
 
   /* Make deploy_path a bind mount, so we can move it later */
   if (mount (deploy_path, deploy_path, NULL, MS_BIND, NULL) < 0)
-    {
+    err (EXIT_FAILURE, "failed to make initial bind mount %s", deploy_path);
-      perrorv ("failed to make initial bind mount %s", deploy_path);
-      exit (EXIT_FAILURE);
-    }
 
   /* chdir to our new root.  We need to do this after bind-mounting it over
    * itself otherwise our cwd is still on the non-bind-mounted filesystem
    * below. */
   if (chdir (deploy_path) < 0)
-    {
+    err (EXIT_FAILURE, "failed to chdir to deploy_path");
-      perrorv ("failed to chdir to deploy_path");
-      exit (EXIT_FAILURE);
-    }
 
   /* Link to the deployment's /var */
   if (mount ("../../var", "var", NULL, MS_MGC_VAL|MS_BIND, NULL) < 0)
-    {
+    err (EXIT_FAILURE, "failed to bind mount ../../var to var");
-      perrorv ("failed to bind mount ../../var to var");
-      exit (EXIT_FAILURE);
-    }
 
   /* If /boot is on the same partition, use a bind mount to make it visible
    * at /boot inside the deployment. */
@@ -251,10 +219,7 @@ main(int argc, char *argv[])
         {
           snprintf (srcpath, sizeof(srcpath), "%s/boot", root_mountpoint);
           if (mount (srcpath, "boot", NULL, MS_BIND, NULL) < 0)
-            {
+            err (EXIT_FAILURE, "failed to bind mount %s to boot", srcpath);
-              perrorv ("failed to bind mount %s to boot", srcpath);
-              exit (EXIT_FAILURE);
-            }
         }
     }
 
@@ -271,31 +236,19 @@ main(int argc, char *argv[])
       if (path_is_on_readonly_fs ("."))
 	{
 	  if (mount (".", ".", NULL, MS_REMOUNT | MS_SILENT, NULL) < 0)
-	    {
+	    err (EXIT_FAILURE, "failed to remount rootfs writable (for overlayfs)");
-	      perrorv ("failed to remount rootfs writable (for overlayfs)");
-	      exit (EXIT_FAILURE);
-	    }
 	}
       
       if (mount ("overlay", "usr", "overlay", 0, usr_ovl_options) < 0)
-	{
+        err (EXIT_FAILURE, "failed to mount /usr overlayfs");
-	  perrorv ("failed to mount /usr overlayfs");
-	  exit (EXIT_FAILURE);
-	}
     }
   else
     {
       /* Otherwise, a read-only bind mount for /usr */
       if (mount ("usr", "usr", NULL, MS_BIND, NULL) < 0)
-	{
+        err (EXIT_FAILURE, "failed to bind mount (class:readonly) /usr");
-	  perrorv ("failed to bind mount (class:readonly) /usr");
-	  exit (EXIT_FAILURE);
-	}
       if (mount ("usr", "usr", NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL) < 0)
-	{
+        err (EXIT_FAILURE, "failed to bind mount (class:readonly) /usr");
-	  perrorv ("failed to bind mount (class:readonly) /usr");
-	  exit (EXIT_FAILURE);
-	}
     }
 
   touch_run_ostree ();
@@ -309,10 +262,7 @@ main(int argc, char *argv[])
        * sysroot, so moving sysroot would also move the deploy location.   In
        * reality attempting mount --move would fail with EBUSY. */
       if (pivot_root (".", "sysroot") < 0)
-        {
+        err (EXIT_FAILURE, "failed to pivot_root to deployment");
-          perrorv ("failed to pivot_root to deployment");
-          exit (EXIT_FAILURE);
-        }
     }
   else
     {
@@ -330,35 +280,22 @@ main(int argc, char *argv[])
        * 3. /sysroot.tmp -> /sysroot
        */
       if (mkdir ("/sysroot.tmp", 0755) < 0)
-        {
+        err (EXIT_FAILURE, "couldn't create temporary sysroot /sysroot.tmp");
-          perrorv ("couldn't create temporary sysroot /sysroot.tmp: ");
-          exit (EXIT_FAILURE);
-        }
 
       if (mount (deploy_path, "/sysroot.tmp", NULL, MS_MOVE, NULL) < 0)
-        {
+        err (EXIT_FAILURE, "failed to MS_MOVE '%s' to '/sysroot.tmp'", deploy_path);
-          perrorv ("failed to MS_MOVE '%s' to '/sysroot.tmp'", deploy_path);
-          exit (EXIT_FAILURE);
-        }
 
       if (mount (root_mountpoint, "sysroot", NULL, MS_MOVE, NULL) < 0)
-        {
+        err (EXIT_FAILURE, "failed to MS_MOVE '%s' to 'sysroot'", root_mountpoint);
-          perrorv ("failed to MS_MOVE '%s' to 'sysroot'", root_mountpoint);
-          exit (EXIT_FAILURE);
-        }
 
       if (mount (".", root_mountpoint, NULL, MS_MOVE, NULL) < 0)
-        {
+        err (EXIT_FAILURE, "failed to MS_MOVE %s to %s", deploy_path, root_mountpoint);
-          perrorv ("failed to MS_MOVE %s to %s", deploy_path, root_mountpoint);
-          exit (EXIT_FAILURE);
-        }
     }
 
   if (getpid() == 1)
     {
       execl ("/sbin/init", "/sbin/init", NULL);
-      perrorv ("failed to exec init inside ostree");
+      err (EXIT_FAILURE, "failed to exec init inside ostree");
-      exit (EXIT_FAILURE);
     }
   else
     {

src/switchroot/ostree-remount.c

@@ -33,6 +33,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/stat.h>
+#include <err.h>
 #include <errno.h>
 
 #include "ostree-mount-util.h"
@@ -49,15 +50,10 @@ maybe_mount_tmpfs_on_var (void)
     return;
 
   if (umount ("/var") < 0 && errno != EINVAL)
-    {
+    warn ("failed to unmount /var prior to mounting tmpfs, mounting over");
-      perror ("failed to unmount /var prior to mounting tmpfs, mounting over");
-    }
 
   if (mount ("tmpfs", "/var", "tmpfs", 0, NULL) < 0)
-    {
+    err (EXIT_FAILURE, "failed to mount tmpfs on /var");
-      perror ("failed to mount tmpfs on /var");
-      exit (EXIT_FAILURE);
-    }
 }
 
 int
@@ -94,10 +90,7 @@ main(int argc, char *argv[])
            * already, then assume things are OK.
            */
           if (errno != EINVAL)
-            {
+            err (EXIT_FAILURE, "failed to remount %s", target);
-              perrorv ("failed to remount %s", target);
-              exit (EXIT_FAILURE);
-            }
 	}
     }