Re: [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 _______________________________________________ Libguestfs mailing list Libguestfs(a)redhat.com https://www.redhat.com/mailman/listinfo/libguestfs