Re: [libvirt] [sandbox 07/10] qemu: use mounts targeting / as root

So far a mount with / as target doesn't change anything: the host / is still the one mounted as /. libvirt-sandbox-init-qemu now detects the presence of a / target in mounts.cfg and mounts it instead of sandbox:root. --- libvirt-sandbox/libvirt-sandbox-init-qemu.c | 69 ++++++++++++++++++++++++++++- 1 file changed, 67 insertions(+), 2 deletions(-) diff --git a/libvirt-sandbox/libvirt-sandbox-init-qemu.c b/libvirt-sandbox/libvirt-sandbox-init-qemu.c index 9acea5f..02fb980 100644 --- a/libvirt-sandbox/libvirt-sandbox-init-qemu.c +++ b/libvirt-sandbox/libvirt-sandbox-init-qemu.c @@ -264,6 +264,70 @@ mount_entry(const char *source, } } +static void +mount_root(const char *path) +{ + int foundRoot = 0; + + /* Loop over mounts.cfg to see if we have a candidate for / */ + mount_mkdir(SANDBOXCONFIGDIR, 0755); + mount_9pfs("sandbox:config", SANDBOXCONFIGDIR, 0755, 1); + + FILE *fp = fopen(SANDBOXCONFIGDIR "/mounts.cfg", "r"); + while (fgets(line, sizeof line, fp) && !foundRoot) { + char *source = line; + char *target = strchr(source, '\t'); + *target = '\0'; + target++; + char *type = strchr(target, '\t'); + *type = '\0'; + type++; + char *opts = strchr(type, '\t'); + *opts = '\0'; + opts++; + char *tmp = strchr(opts, '\n'); + *tmp = '\0'; + + if (STREQ(target, "/")) { + int needsDev = strncmp(source, "/dev/", 5) == 0; + + if (debug) + fprintf(stderr, "libvirt-sandbox-init-qemu: found root from %s\n", + source); + + /* In this case, we need to have a /dev before the chroot */ + if (needsDev) { + mount_other("/proc", "proc", 0755); + mount_other("/dev", "tmpfs", 0755);

+ } + + mount_entry(source, path, type, opts); + + if (needsDev && umount("/dev") < 0) { + fprintf(stderr, + "libvirt-sandbox-init-qemu: %s: " + "cannot unmount temporary /dev: %s\n", + __func__, strerror(errno)); + exit_poweroff(); + }

+ foundRoot = 1; + } + } + fclose(fp); + + if (umount(SANDBOXCONFIGDIR) < 0) { + fprintf(stderr, + "libvirt-sandbox-init-qemu: %s: " + "cannot unmount temporary %s: %s\n", + __func__, SANDBOXCONFIGDIR, strerror(errno)); + exit_poweroff(); + } + + /* If we couldn't get a / in the mounts, then use the host one */ + if (!foundRoot) + mount_9pfs("sandbox:root", path, 0755, 1); +} + int main(int argc ATTR_UNUSED, char **argv ATTR_UNUSED) { @@ -308,7 +372,7 @@ main(int argc ATTR_UNUSED, char **argv ATTR_UNUSED) if (debug) fprintf(stderr, "libvirt-sandbox-init-qemu: mounting new root on /tmproot\n"); - mount_9pfs("sandbox:root", "/tmproot", 0755, 1); + mount_root("/tmproot"); /* Note that pivot_root won't work. See the note in * Documentation/filesystems/ramfs-rootfs-initramfs.txt @@ -412,7 +476,8 @@ main(int argc ATTR_UNUSED, char **argv ATTR_UNUSED) fprintf(stderr, "libvirt-sandbox-init-qemu: %s: %s -> %s (%s, %s)\n", __func__, source, target, type, opts); - mount_entry(source, target, type, opts); + if (STREQ(target, "/"))

+ mount_entry(source, target, type, opts); } fclose(fp);