[CRIU] [PATCH v4 2/3] mount: Forced mount unmounted binfmt_misc to do not lost its content
Pavel Emelyanov
xemul at virtuozzo.com
Tue Aug 2 07:09:05 PDT 2016
On 08/02/2016 04:34 PM, Kirill Tkhai wrote:
> On 02.08.2016 16:31, Pavel Emelyanov wrote:
>> On 08/02/2016 04:25 PM, Kirill Tkhai wrote:
>>
>>>>
>>>>> + parent = t;
>>>>> + break;
>>>>> + }
>>>>> + }
>>>>> + if (&t->siblings == &parent->children)
>>>>> + break;
>>>>> + }
>>>>> +
>>>>> + mi->nsid = parent->nsid;
>>>>> + mi->parent = parent;
>>>>> + mi->parent_mnt_id = parent->mnt_id;
>>>>> + mi->next = parent->next;
>>>>> + parent->next = mi;
>>>>> + list_add(&mi->siblings, &parent->children);
>>>>> + pr_info("Add cr-time mountpoint %s with parent %s(%u)\n",
>>>>> + mi->mountpoint, parent->mountpoint, parent->mnt_id);
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +
>>>>> /* Is it mounted w or w/o the newinstance option */
>>>>> static int devpts_parse(struct mount_info *pm)
>>>>> {
>>>>> @@ -1272,6 +1320,65 @@ static int devtmpfs_restore(struct mount_info *pm)
>>>>> return ret;
>>>>> }
>>>>>
>>>>> +static int try_mount_binfmt_misc(struct ns_id *ns, unsigned int *s_dev)
>>>>> +{
>>>>> + int num, mnt_fd, ret, exit_code = -1;
>>>>> + struct dirent *de;
>>>>> + struct stat st;
>>>>> + DIR *dir;
>>>>> +
>>>>> + ret = switch_ns(ns->ns_pid, &mnt_ns_desc, &mnt_fd);
>>>>> + if (ret < 0) {
>>>>> + pr_err("Can't switch mnt_ns\n");
>>>>> + goto out;
>>>>> + }
>>>>> +
>>>>> + ret = mount("binfmt_misc", BINFMT_MISC_HOME, "binfmt_misc", 0, NULL);
>>>>> + if (ret < 0) {
>>>>> + if (errno == EPERM) {
>>>>> + pr_info("Can't mount binfmt_misc: EPERM. Running in user_ns?\n");
>>>>> + exit_code = 0;
>>>>> + goto restore_ns;
>>>>> + }
>>>>> + if (errno != EBUSY && errno != ENODEV && errno != ENOENT) {
>>>>> + pr_perror("Can't mount binfmt_misc");
>>>>> + goto restore_ns;
>>>>> + }
>>>>> + pr_info("Prepare binfmt_misc: skipping(%d)\n", errno);
>>>>> + } else {
>>>>> + dir = opendir(BINFMT_MISC_HOME);
>>>>> + if (!dir) {
>>>>> + pr_perror("Can't read binfmt_misc dir");
>>>>> + goto restore_ns;
>>>>> + }
>>>>> +
>>>>> + num = 0;
>>>>> + /* ".", "..", "register", "status" */
>>>>> + while (num <= 4 && (de = readdir(dir)) != NULL)
>>>>> + num++;
>>>>> + closedir(dir);
>>>>> + if (num <= 4) {
>>>>> + /* No entries */
>>>>> + if (umount(BINFMT_MISC_HOME) < 0)
>>>>> + pr_perror("Can't umount "BINFMT_MISC_HOME"\n");
>>>>> + } else {
>>>>> + if (stat(BINFMT_MISC_HOME, &st) < 0)
>>>>> + pr_perror("Can't stat on binfmt_misc path\n");
>>>>> + else {
>>>>> + *s_dev = st.st_dev;
>>>>> + exit_code = 1;
>>>>> + }
>>>>> + goto restore_ns;
>>>>> + }
>>>>
>>>> What does this else branch do? Why can't we just add the entry and
>>>> let ->dump callback do whatever is appropriate?
>>>
>>> This branch searches for dev of newly mounted binfmt_misc, because
>>
>> It also calls readdir(). What for?
>
> There is a commentary. If no entries is registered, then we don't want to have forced mounted binfmt_misc.
Why not off-load this decision to ->dump callback of binfmt_misc? It doesn't
produce any images if the binfmt is either empty or not virtualized.
>>> ->dump callback checks for mount is virtual or not. I can pass 0 as
>>> dev here if you want. Do you?
>>
>> No, I don't. Getting the mount's dev is needed.
>>
>>>>> + }
>>>>> +
>>>>> + exit_code = 0;
>>>>> +restore_ns:
>>>>> + ret = restore_ns(mnt_fd, &mnt_ns_desc);
>>>>> +out:
>>>>> + return ret ? -1 : exit_code;
>>>>> +}
>>>>> +
>>>>> static int binfmt_misc_virtual(struct mount_info *pm)
>>>>> {
>>>>> return kerndat_fs_virtualized(KERNDAT_FS_STAT_BINFMT_MISC, pm->s_dev);
>>>>> @@ -1873,6 +1980,11 @@ static int dump_one_mountpoint(struct mount_info *pm, struct cr_img *img)
>>>>> if (!pm->dumped && dump_one_fs(pm))
>>>>> return -1;
>>>>>
>>>>> + if (pm->mnt_id == 0) {
>>>>> + pr_info("Skip dumping cr-time mountpoint: %s\n", pm->mountpoint);
>>>>> + return 0;
>>>>> + }
>>>>> +
>>>>> me.mnt_id = pm->mnt_id;
>>>>> me.root_dev = pm->s_dev;
>>>>> me.parent_mnt_id = pm->parent_mnt_id;
>>>>> @@ -1931,7 +2043,8 @@ static void free_mntinfo(struct mount_info *pms)
>>>>>
>>>>> struct mount_info *collect_mntinfo(struct ns_id *ns, bool for_dump)
>>>>> {
>>>>> - struct mount_info *pm;
>>>>> + struct mount_info *pm, *mi;
>>>>> + int ret;
>>>>>
>>>>> pm = parse_mountinfo(ns->ns_pid, ns, for_dump);
>>>>> if (!pm) {
>>>>> @@ -1943,6 +2056,22 @@ struct mount_info *collect_mntinfo(struct ns_id *ns, bool for_dump)
>>>>> if (ns->mnt.mntinfo_tree == NULL)
>>>>> goto err;
>>>>>
>>>>> + if (for_dump && ns->type == NS_ROOT) {
>>>>> + for (mi = pm; mi != NULL; mi = mi->next) {
>>>>> + if (strcmp(mi->fstype->name, "binfmt_misc") == 0)
>>>>> + break;
>>>>> + }
>>>>
>>>> You don't have to search for the entry, just declare the ->parse callback
>>>> and set the boolean flag. Or add flag (or count) on fstype struct and count
>>>> for mountpoints of desired fstype.
>>>
>>> What is "just declare the ->parse callback"?
>>
>> criu/mount.c, line 1672
>>
>> }, {
>> .name = "devpts",
>> .parse = devpts_parse, <<<< this thing gets called when reading an entry in /proc/pid/mountinfo
>> .code = FSTYPE__DEVPTS,
>> }, {
>
> And global boolean variable "binfmt_misc_collected"?
It's arguable. For aufs we have opts.aufs bit. For ... overlayfs (?) we have similar.
We can add binfmt_misc to opts, or have separate entity to ask "whether fs X was
mounted" for.
>>
>>>>> + if (!mi) {
>>>>> + unsigned int s_dev = 0;
>>>>> + ret = try_mount_binfmt_misc(ns, &s_dev);
>>>>> + if (ret < 0)
>>>>> + return NULL;
>>>>> + if (ret > 0 && add_cr_time_mount(ns->mnt.mntinfo_tree, "binfmt_misc",
>>>>> + BINFMT_MISC_HOME, s_dev) < 0)
>>>>> + return NULL;
>>>>> + }
>>>>> + }
>>>>> +
>>>>> ns->mnt.mntinfo_list = pm;
>>>>> return pm;
>>>>> err:
>>>>> @@ -3683,4 +3812,28 @@ int dump_mnt_namespaces(void)
>>>>> return 0;
>>>>> }
>>>>>
>>>>> +void clean_cr_time_mounts(void)
>>>>> +{
>>>>> + struct mount_info *mi;
>>>>> + int mnt_fd, ret;
>>>>> +
>>>>> + for (mi = mntinfo; mi; mi = mi->next) {
>>>>> + if (mi->mnt_id)
>>>>> + continue;
>>>>> + ret = switch_ns(mi->nsid->ns_pid, &mnt_ns_desc, &mnt_fd);
>>>>> + if (ret) {
>>>>> + pr_err("Can't switch to pid's %u mnt_ns\n", mi->nsid->ns_pid);
>>>>> + continue;
>>>>> + }
>>>>> +
>>>>> + if (umount(mi->mountpoint) < 0)
>>>>> + pr_perror("Can't umount forced mount %s\n", mi->mountpoint);
>>>>> +
>>>>> + if (restore_ns(mnt_fd, &mnt_ns_desc)) {
>>>>
>>>> Can we restore it once outside the loop?
>>>
>>> How can we restore hypothetical several forced mounts without a loop?
>>
>> I mean restore_ns() :\ Switch ns-s one by one and return to original one once.
>
> Will open_proc() called in switch_ns() work in this case?
I don't know, that's why I'm asking. IIRC we have loops with switch_ns()-s
inside over the code.
-- Pavel
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