[lxc-devel] [PATCH 1/2] Setup devtmpfs and /dev for autodev bind mounts.
Michael H. Warfield
mhw at WittsEnd.com
Tue Nov 19 21:47:39 UTC 2013
On Tue, 2013-11-19 at 14:53 -0600, Serge Hallyn wrote:
> Quoting Michael H. Warfield (mhw at WittsEnd.com):
> > If autodev is not specifically set to 0 or 1, attempts to determine if
> > systemd is being utilized and forces autodev=1 to prevent host system
> > conflicts and collisions.
> >
> > If autodev is enabled and the host /dev is mounted with devtmpfs
> > or /dev/.lxc is mounted with another file system...
> >
> > Each container created by a privileged user gets a /dev directory
> > mapped off the host /dev here:
> >
> > /dev/.lxc/${name}.$( hash $lxcpath/$name )
> >
> > Each container created by a non-privileged user gets a /dev/directory
> > mapped off the host /dev here:
> >
> > /dev/.lxc/user/${name}.$( hash $lxcpath/$name )
> >
> > The /dev/.lxc/user is mode 1777 to allow unpriv access.
> >
> > The /dev/.lxc/{containerdev} is bind mounted into the container /dev.
> >
> > Fallback on failure is to mount tmpfs into the container /dev.
> >
> > A symlink is created from $lxcpath/$name/rootfs.dev back to the /dev
> > relative directory to provid a code consistent reference for updating
> > container devs.
>
> Hi Michael,
>
> I haven't run it, but looking over the code in detail, it looks good
> to me. I know Stéphane in the past has objected to trying to autodetect
> systemd based containers. IMO it'd be fine to expect the templates to
> set lxc.autodev, as I worry about building distro-detecting hacks into
> core lxc, but unless Stéphane objects I don't care enough in this case
> to nack it.
> Did you consider this patch good enough to apply, or was this still an
> RFC? I'm happy either way.
I do consider it ready, which is why I, belatedly, signed off on it.
> Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>
Regards,
Mike
>
> > ---
> > src/lxc/conf.c | 369 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
> > src/lxc/conf.h | 4 +-
> > src/lxc/start.c | 2 +-
> > 3 files changed, 363 insertions(+), 12 deletions(-)
> >
> > diff --git a/src/lxc/conf.c b/src/lxc/conf.c
> > index a756731..d17cb2a 100644
> > --- a/src/lxc/conf.c
> > +++ b/src/lxc/conf.c
> > @@ -29,6 +29,7 @@
> > #include <string.h>
> > #include <dirent.h>
> > #include <unistd.h>
> > +#include <inttypes.h>
> > #include <sys/wait.h>
> > #include <sys/syscall.h>
> > #include <time.h>
> > @@ -1164,20 +1165,275 @@ static int setup_rootfs_pivot_root(const char *rootfs, const char *pivotdir)
> > return 0;
> > }
> >
> > +
> > +/*
> > + * Note: This is a verbatum copy of what is in monitor.c. We're just
> > + * usint it here to generate a safe subdirectory in /dev/ for the
> > + * containers /dev/
> > + */
> > +
> > +/* Note we don't use SHA-1 here as we don't want to depend on HAVE_GNUTLS.
> > + * FNV has good anti collision properties and we're not worried
> > + * about pre-image resistance or one-way-ness, we're just trying to make
> > + * the name unique in the 108 bytes of space we have.
> > + */
> > +#define FNV1A_64_INIT ((uint64_t)0xcbf29ce484222325ULL)
> > +static uint64_t fnv_64a_buf(void *buf, size_t len, uint64_t hval)
> > +{
> > + unsigned char *bp;
> > +
> > + for(bp = buf; bp < (unsigned char *)buf + len; bp++)
> > + {
> > + /* xor the bottom with the current octet */
> > + hval ^= (uint64_t)*bp;
> > +
> > + /* gcc optimised:
> > + * multiply by the 64 bit FNV magic prime mod 2^64
> > + */
> > + hval += (hval << 1) + (hval << 4) + (hval << 5) +
> > + (hval << 7) + (hval << 8) + (hval << 40);
> > + }
> > +
> > + return hval;
> > +}
> > +
> > +/*
> > + * Check to see if a directory has something mounted on it and,
> > + * if it does, return the fstype.
> > + *
> > + * Code largely based on detect_shared_rootfs below
> > + *
> > + * Returns: # of matching entries in /proc/self/mounts
> > + * if != 0 fstype is filled with the last filesystem value.
> > + * if == 0 no matches found, fstype unchanged.
> > + *
> > + * ToDo: Maybe return the mount options in another parameter...
> > + */
> > +
> > +#define LINELEN 4096
> > +#define MAX_FSTYPE_LEN 128
> > +int mount_check_fs( const char *dir, char *fstype )
> > +{
> > + char buf[LINELEN], *p;
> > + struct stat s;
> > + FILE *f;
> > + int found_fs = 0;
> > + char *p2;
> > +
> > + DEBUG("entering mount_check_fs for %s\n", dir);
> > +
> > + if ( 0 != access(dir, F_OK) || 0 != stat(dir, &s) || 0 == S_ISDIR(s.st_mode) ) {
> > + return 0;
> > + }
> > +
> > + process_lock();
> > + f = fopen("/proc/self/mounts", "r");
> > + process_unlock();
> > + if (!f)
> > + return 0;
> > + while ((p = fgets(buf, LINELEN, f))) {
> > + p = index(buf, ' ');
> > + if( !p )
> > + continue;
> > + *p = '\0';
> > + p2 = p + 1;
> > +
> > + p = index(p2, ' ');
> > + if( !p )
> > + continue;
> > + *p = '\0';
> > +
> > + /* Compare the directory in the entry to desired */
> > + if( strcmp( p2, dir ) ) {
> > + continue;
> > + }
> > +
> > + p2 = p + 1;
> > + p = index( p2, ' ');
> > + if( !p )
> > + continue;
> > + *p = '\0';
> > +
> > + ++found_fs;
> > +
> > + if( fstype ) {
> > + strncpy( fstype, p2, MAX_FSTYPE_LEN - 1 );
> > + fstype [ MAX_FSTYPE_LEN - 1 ] = '\0';
> > + }
> > + }
> > +
> > + process_lock();
> > + fclose(f);
> > + process_unlock();
> > +
> > + DEBUG("mount_check_fs returning %d last %s\n", found_fs, fstype);
> > +
> > + return found_fs;
> > +}
> > +
> > +/*
> > + * Locate a devtmpfs mount (should be on /dev) and create a container
> > + * subdirectory on it which we can then bind mount to the container
> > + * /dev instead of mounting a tmpfs there.
> > + * If we fail, return NULL.
> > + * Else return the pointer to the name buffer with the string to
> > + * the devtmpfs subdirectory.
> > + */
> > +
> > +char *mk_devtmpfs(const char *name, char *path, const char *lxcpath)
> > +{
> > + int ret;
> > + struct stat s;
> > + char tmp_path[MAXPATHLEN];
> > + char fstype[MAX_FSTYPE_LEN];
> > + char *base_path = "/dev/.lxc";
> > + char *user_path = "/dev/.lxc/user";
> > + uint64_t hash;
> > +
> > + if ( 0 != access(base_path, F_OK) || 0 != stat(base_path, &s) || 0 == S_ISDIR(s.st_mode) ) {
> > + /* This is just making /dev/.lxc it better work or we're done */
> > + ret = mkdir(base_path, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
> > + if ( ret ) {
> > + SYSERROR( "Unable to create /dev/.lxc for autodev" );
> > + return NULL;
> > + }
> > + }
> > +
> > + /*
> > + * Programmers notes:
> > + * We can not do mounts in this area of code that we want
> > + * to be visible in the host. Consequently, /dev/.lxc must
> > + * be set up earlier if we need a tmpfs mounted there.
> > + * That only affects the rare cases where autodev is enabled
> > + * for a container and devtmpfs is not mounted on /dev in the
> > + * host. In that case, we'll fall back to the old method
> > + * of mounting a tmpfs in the container and have no visibility
> > + * into the container /dev.
> > + */
> > + if( ! mount_check_fs( "/dev", fstype )
> > + || strcmp( "devtmpfs", fstype ) ) {
> > + /* Either /dev was not mounted or was not devtmpfs */
> > +
> > + if ( ! mount_check_fs( "/dev/.lxc", NULL ) ) {
> > + /*
> > + * /dev/.lxc is not already mounted
> > + * Doing a mount here does no good, since
> > + * it's not visible in the host.
> > + */
> > +
> > + ERROR("/dev/.lxc is not setup - taking fallback" );
> > + return NULL;
> > + }
> > + }
> > +
> > + if ( 0 != access(user_path, F_OK) || 0 != stat(user_path, &s) || 0 == S_ISDIR(s.st_mode) ) {
> > + /*
> > + * This is making /dev/.lxc/user path for non-priv users.
> > + * If this doesn't work, we'll have to fall back in the
> > + * case of non-priv users. It's mode 1777 like /tmp.
> > + */
> > + ret = mkdir(user_path, S_IRWXU | S_IRWXG | S_IRWXO | S_ISVTX);
> > + if ( ret ) {
> > + /* Issue an error but don't fail yet! */
> > + ERROR("Unable to create /dev/.lxc/user");
> > + }
> > + /* Umask tends to screw us up here */
> > + chmod(user_path, S_IRWXU | S_IRWXG | S_IRWXO | S_ISVTX);
> > + }
> > +
> > + /*
> > + * Since the container name must be unique within a given
> > + * lxcpath, we're going to use a hash of the path
> > + * /lxcpath/name as our hash name in /dev/.lxc/
> > + */
> > +
> > + ret = snprintf(tmp_path, MAXPATHLEN, "%s/%s", lxcpath, name);
> > + if (ret < 0 || ret >= MAXPATHLEN)
> > + return NULL;
> > +
> > + hash = fnv_64a_buf(tmp_path, ret, FNV1A_64_INIT);
> > +
> > + ret = snprintf(tmp_path, MAXPATHLEN, "%s/%s.%016" PRIx64, base_path, name, hash);
> > + if (ret < 0 || ret >= MAXPATHLEN)
> > + return NULL;
> > +
> > + if ( 0 != access(tmp_path, F_OK) || 0 != stat(tmp_path, &s) || 0 == S_ISDIR(s.st_mode) ) {
> > + ret = mkdir(tmp_path, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
> > + if ( ret ) {
> > + /* Something must have failed with the base_path...
> > + * Maybe unpriv user. Try user_path now... */
> > + INFO("Setup in /dev/.lxc failed. Trying /dev/.lxc/user." );
> > +
> > + ret = snprintf(tmp_path, MAXPATHLEN, "%s/%s.%016" PRIx64, user_path, name, hash);
> > + if (ret < 0 || ret >= MAXPATHLEN)
> > + return NULL;
> > +
> > + if ( 0 != access(tmp_path, F_OK) || 0 != stat(tmp_path, &s) || 0 == S_ISDIR(s.st_mode) ) {
> > + ret = mkdir(tmp_path, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
> > + if ( ret ) {
> > + ERROR("Container /dev setup in host /dev failed - taking fallback" );
> > + return NULL;
> > + }
> > + }
> > + }
> > + }
> > +
> > + strcpy( path, tmp_path );
> > + return path;
> > +}
> > +
> > +
> > /*
> > * Do we want to add options for max size of /dev and a file to
> > * specify which devices to create?
> > */
> > -static int mount_autodev(char *root)
> > +static int mount_autodev(const char *name, char *root, const char *lxcpath)
> > {
> > int ret;
> > + struct stat s;
> > char path[MAXPATHLEN];
> > + char host_path[MAXPATHLEN];
> > + char devtmpfs_path[MAXPATHLEN];
> >
> > INFO("Mounting /dev under %s\n", root);
> > +
> > + ret = snprintf(host_path, MAXPATHLEN, "%s/%s/rootfs.dev", lxcpath, name);
> > + if (ret < 0 || ret > MAXPATHLEN)
> > + return -1;
> > +
> > ret = snprintf(path, MAXPATHLEN, "%s/dev", root);
> > if (ret < 0 || ret > MAXPATHLEN)
> > return -1;
> > - ret = mount("none", path, "tmpfs", 0, "size=100000");
> > +
> > + if (mk_devtmpfs( name, devtmpfs_path, lxcpath ) ) {
> > + /*
> > + * Get rid of old links and directoriess
> > + * This could be either a symlink and we remove it,
> > + * or an empty directory and we remove it,
> > + * or non-existant and we don't care,
> > + * or a non-empty directory, and we will then emit an error
> > + * but we will not fail out the process.
> > + */
> > + unlink( host_path );
> > + rmdir( host_path );
> > + ret = symlink(devtmpfs_path, host_path);
> > +
> > + if ( ret < 0 ) {
> > + SYSERROR("WARNING: Failed to create symlink '%s'->'%s'\n", host_path, devtmpfs_path);
> > + }
> > + DEBUG("Bind mounting %s to %s", devtmpfs_path , path );
> > + ret = mount(devtmpfs_path, path, NULL, MS_BIND, 0 );
> > + } else {
> > + /* Only mount a tmpfs on here if we don't already a mount */
> > + if ( ! mount_check_fs( host_path, NULL ) ) {
> > + DEBUG("Mounting tmpfs to %s", host_path );
> > + ret = mount("none", path, "tmpfs", 0, "size=100000");
> > + } else {
> > + /* This allows someone to manually set up a mount */
> > + DEBUG("Bind mounting %s to %s", host_path, path );
> > + ret = mount(host_path , path, NULL, MS_BIND, 0 );
> > + }
> > + }
> > if (ret) {
> > SYSERROR("Failed to mount /dev at %s\n", root);
> > return -1;
> > @@ -1185,10 +1441,16 @@ static int mount_autodev(char *root)
> > ret = snprintf(path, MAXPATHLEN, "%s/dev/pts", root);
> > if (ret < 0 || ret >= MAXPATHLEN)
> > return -1;
> > - ret = mkdir(path, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
> > - if (ret) {
> > - SYSERROR("Failed to create /dev/pts in container");
> > - return -1;
> > + /*
> > + * If we are running on a devtmpfs mapping, dev/pts may already exist.
> > + * If not, then create it and exit if that fails...
> > + */
> > + if ( 0 != access(path, F_OK) || 0 != stat(path, &s) || 0 == S_ISDIR(s.st_mode) ) {
> > + ret = mkdir(path, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
> > + if (ret) {
> > + SYSERROR("Failed to create /dev/pts in container");
> > + return -1;
> > + }
> > }
> >
> > INFO("Mounted /dev under %s\n", root);
> > @@ -2369,6 +2631,7 @@ struct lxc_conf *lxc_conf_init(void)
> >
> > new->loglevel = LXC_LOG_PRIORITY_NOTSET;
> > new->personality = -1;
> > + new->autodev = -1;
> > new->console.log_path = NULL;
> > new->console.log_fd = -1;
> > new->console.path = NULL;
> > @@ -3136,7 +3399,89 @@ int ttys_shift_ids(struct lxc_conf *c)
> > return 0;
> > }
> >
> > -int lxc_setup(const char *name, struct lxc_conf *lxc_conf, const char *lxcpath, struct cgroup_process_info *cgroup_info)
> > +/*
> > + * This routine is called when the configuration does not already specify a value
> > + * for autodev (mounting a file system on /dev and populating it in a container).
> > + * If a hard override value has not be specified, then we try to apply some
> > + * heuristics to determine if we should switch to autodev mode.
> > + *
> > + * For instance, if the container has an /etc/systemd/system directory then it
> > + * is probably running systemd as the init process and it needs the autodev
> > + * mount to prevent it from mounting devtmpfs on /dev on it's own causing conflicts
> > + * in the host.
> > + *
> > + * We may also want to enable autodev if the host has devtmpfs mounted on its
> > + * /dev as this then enable us to use subdirectories under /dev for the container
> > + * /dev directories and we can fake udev devices.
> > + */
> > +struct start_args {
> > + char *const *argv;
> > +};
> > +
> > +#define MAX_SYMLINK_DEPTH 32
> > +
> > +int check_autodev( const char *rootfs, void *data )
> > +{
> > + struct start_args *arg = data;
> > + int ret;
> > + int loop_count = 0;
> > + struct stat s;
> > + char absrootfs[MAXPATHLEN];
> > + char path[MAXPATHLEN];
> > + char abs_path[MAXPATHLEN];
> > + char *command = "/sbin/init";
> > +
> > + if (rootfs == NULL || strlen(rootfs) == 0)
> > + return -2;
> > +
> > + if (!realpath(rootfs, absrootfs))
> > + return -2;
> > +
> > + if( arg && arg->argv[0] ) {
> > + command = arg->argv[0];
> > + DEBUG("Set exec command to %s\n", command );
> > + }
> > +
> > + strncpy( path, command, MAXPATHLEN-1 );
> > +
> > + if ( 0 != access(path, F_OK) || 0 != stat(path, &s) )
> > + return -2;
> > +
> > + /* Dereference down the symlink merry path testing as we go. */
> > + /* If anything references systemd in the path - set autodev! */
> > + /* Renormalize to the rootfs before each dereference */
> > + /* Relative symlinks should fall out in the wash even with .. */
> > + while( 1 ) {
> > + if ( strstr( path, "systemd" ) ) {
> > + INFO("Container with systemd init detected - enabling autodev!");
> > + return 1;
> > + }
> > +
> > + ret = snprintf(abs_path, MAXPATHLEN-1, "%s/%s", absrootfs, path);
> > + if (ret < 0 || ret > MAXPATHLEN)
> > + return -2;
> > +
> > + ret = readlink( abs_path, path, MAXPATHLEN-1 );
> > +
> > + if ( ( ret <= 0 ) || ( ++loop_count > MAX_SYMLINK_DEPTH ) ) {
> > + break; /* Break out for other tests */
> > + }
> > + path[ret] = '\0';
> > + }
> > +
> > + /*
> > + * Add future checks here.
> > + * Return positive if we should go autodev
> > + * Return 0 if we should NOT go autodev
> > + * Return negative if we encounter an error or can not determine...
> > + */
> > +
> > + /* All else fails, we don't need autodev */
> > + INFO("Autodev not required.");
> > + return 0;
> > +}
> > +
> > +int lxc_setup(const char *name, struct lxc_conf *lxc_conf, const char *lxcpath, struct cgroup_process_info *cgroup_info, void *data)
> > {
> > if (setup_utsname(lxc_conf->utsname)) {
> > ERROR("failed to setup the utsname for '%s'", name);
> > @@ -3158,8 +3503,12 @@ int lxc_setup(const char *name, struct lxc_conf *lxc_conf, const char *lxcpath,
> > return -1;
> > }
> >
> > - if (lxc_conf->autodev) {
> > - if (mount_autodev(lxc_conf->rootfs.mount)) {
> > + if (lxc_conf->autodev < 0) {
> > + lxc_conf->autodev = check_autodev(lxc_conf->rootfs.mount, data);
> > + }
> > +
> > + if (lxc_conf->autodev > 0) {
> > + if (mount_autodev(name, lxc_conf->rootfs.mount, lxcpath)) {
> > ERROR("failed to mount /dev in the container");
> > return -1;
> > }
> > @@ -3197,7 +3546,7 @@ int lxc_setup(const char *name, struct lxc_conf *lxc_conf, const char *lxcpath,
> > return -1;
> > }
> >
> > - if (lxc_conf->autodev) {
> > + if (lxc_conf->autodev > 0) {
> > if (run_lxc_hooks(name, "autodev", lxc_conf, lxcpath, NULL)) {
> > ERROR("failed to run autodev hooks for container '%s'.", name);
> > return -1;
> > diff --git a/src/lxc/conf.h b/src/lxc/conf.h
> > index 940d493..090c5b3 100644
> > --- a/src/lxc/conf.h
> > +++ b/src/lxc/conf.h
> > @@ -356,7 +356,9 @@ extern int lxc_clear_hooks(struct lxc_conf *c, const char *key);
> >
> > struct cgroup_process_info;
> > extern int lxc_setup(const char *name, struct lxc_conf *lxc_conf,
> > - const char *lxcpath, struct cgroup_process_info *cgroup_info);
> > + const char *lxcpath,
> > + struct cgroup_process_info *cgroup_info,
> > + void *data);
> >
> > extern void lxc_rename_phys_nics_on_shutdown(struct lxc_conf *conf);
> >
> > diff --git a/src/lxc/start.c b/src/lxc/start.c
> > index 3b2ba8f..3d2bc86 100644
> > --- a/src/lxc/start.c
> > +++ b/src/lxc/start.c
> > @@ -553,7 +553,7 @@ static int do_start(void *data)
> > #endif
> >
> > /* Setup the container, ip, names, utsname, ... */
> > - if (lxc_setup(handler->name, handler->conf, handler->lxcpath, handler->cgroup)) {
> > + if (lxc_setup(handler->name, handler->conf, handler->lxcpath, handler->cgroup, handler->data) ){
> > ERROR("failed to setup the container");
> > goto out_warn_father;
> > }
> > --
> > 1.8.3.1
> >
> >
> > --
> > Michael H. Warfield (AI4NB) | (770) 978-7061 | mhw at WittsEnd.com
> > /\/\|=mhw=|\/\/ | (678) 463-0932 | http://www.wittsend.com/mhw/
> > NIC whois: MHW9 | An optimist believes we live in the best of all
> > PGP Key: 0x674627FF | possible worlds. A pessimist is sure of it!
> >
>
>
>
> > ------------------------------------------------------------------------------
> > November Webinars for C, C++, Fortran Developers
> > Accelerate application performance with scalable programming models. Explore
> > techniques for threading, error checking, porting, and tuning. Get the most
> > from the latest Intel processors and coprocessors. See abstracts and register
> > http://pubads.g.doubleclick.net/gampad/clk?id=60136231&iu=/4140/ostg.clktrk
>
> > _______________________________________________
> > Lxc-devel mailing list
> > Lxc-devel at lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/lxc-devel
>
>
--
Michael H. Warfield (AI4NB) | (770) 978-7061 | mhw at WittsEnd.com
/\/\|=mhw=|\/\/ | (678) 463-0932 | http://www.wittsend.com/mhw/
NIC whois: MHW9 | An optimist believes we live in the best of all
PGP Key: 0x674627FF | possible worlds. A pessimist is sure of it!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 482 bytes
Desc: This is a digitally signed message part
URL: <http://lists.linuxcontainers.org/pipermail/lxc-devel/attachments/20131119/b031cb0d/attachment.pgp>
More information about the lxc-devel
mailing list