[Libguestfs] [PATCH supermin] init: Delete initramfs files before chrooting into the appliance.
After supermin has finished running, the initramfs files sit around
occupying swappable memory but serving no further purpose.
This saves a little memory, at the cost of about 1ms of extra boot
time.
---
init/init.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 48 insertions(+), 2 deletions(-)
diff --git a/init/init.c b/init/init.c
index 733d66e..5ac53e9 100644
--- a/init/init.c
+++ b/init/init.c
@@ -1,5 +1,5 @@
/* supermin-helper reimplementation in C.
- * Copyright (C) 2009-2014 Red Hat Inc.
+ * Copyright (C) 2009-2016 Red Hat Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -80,6 +80,7 @@ static void mount_proc (void);
static void print_uptime (void);
static void read_cmdline (void);
static void insmod (const char *filename);
+static void delete_initramfs_files (void);
static void show_directory (const char *dir);
static char cmdline[1024];
@@ -264,9 +265,12 @@ main ()
exit (EXIT_FAILURE);
}
+ if (!quiet)
+ fprintf (stderr, "supermin: deleting initramfs files\n");
+ delete_initramfs_files ();
+
/* Note that pivot_root won't work. See the note in
* Documentation/filesystems/ramfs-rootfs-initramfs.txt
- * We could remove the old initramfs files, but let's not bother.
*/
if (!quiet)
fprintf (stderr, "supermin: chroot\n");
@@ -396,6 +400,48 @@ read_cmdline (void)
cmdline[len-1] = '\0';
}
+/* By deleting the files in the initramfs before we chroot, we save a
+ * little bit of memory (or quite a lot of memory if the user is using
+ * unstripped kmods).
+ *
+ * We only delete files in the root directory. We don't delete
+ * directories because they only take a tiny amount of space and
+ * because we must not delete any mountpoints, especially not /root
+ * where we are about to chroot.
+ *
+ * We don't recursively look for files because that would be too
+ * complex and risky, and the normal supermin initramfs doesn't have
+ * any files except in the root directory.
+ */
+static void
+delete_initramfs_files (void)
+{
+ DIR *dir;
+ struct dirent *d;
+ struct stat statbuf;
+
+ if (chdir ("/") == -1) {
+ perror ("chdir: /");
+ return;
+ }
+
+ dir = opendir (".");
+ if (!dir) {
+ perror ("opendir: /");
+ return;
+ }
+
+ while ((d = readdir (dir)) != NULL) {
+ /* "." and ".." are directories, so the S_ISREG test ignores
them. */
+ if (lstat (d->d_name, &statbuf) >= 0 && S_ISREG (statbuf.st_mode))
{
+ if (unlink (d->d_name) == -1)
+ perror (d->d_name);
+ }
+ }
+
+ closedir (dir);
+}
+
/* Display a directory on stderr. This is used for debugging only. */
static char
dirtype (int dt)
--
2.7.4