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mount: allow to dump content even if a part of fs is overmounted (v3)

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for that the mount point is bind-mounted in a temporary place.

v2: * check, that the fs you get access to at the end is _really_ the
      one you wanted to
    * use switch_ns/restore_ns helpers
v3: reuse code of __open_mountpoint and a few small cleanups

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
This commit is contained in:
Andrey Vagin 2013-08-01 17:17:03 +04:00 committed by Pavel Emelyanov
parent 2d631b4562
commit 65d3545945
1 changed files with 88 additions and 20 deletions
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108
mount.c
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@ -197,47 +197,48 @@ static struct mount_info *mnt_build_tree(struct mount_info *list)
return tree;
}
static DIR *open_mountpoint(struct mount_info *pm)
/*
* mnt_fd is a file descriptor on the mountpoint, which is closed in an error case.
* If mnt_fd is -1, the mountpoint will be opened by this function.
*/
static DIR *__open_mountpoint(struct mount_info *pm, int mnt_fd)
{
int fd, ret;
char path[PATH_MAX + 1];
struct stat st;
DIR *fdir;
int ret;
if (!list_empty(&pm->children)) {
pr_err("Something is mounted on top of %s\n", pm->fstype->name);
return NULL;
if (mnt_fd == -1) {
snprintf(path, sizeof(path), ".%s", pm->mountpoint);
mnt_fd = openat(mntns_root, path, O_RDONLY);
if (mnt_fd < 0) {
pr_perror("Can't open %s", pm->mountpoint);
return NULL;
}
}
snprintf(path, sizeof(path), ".%s", pm->mountpoint);
fd = openat(mntns_root, path, O_RDONLY);
if (fd < 0) {
pr_perror("Can't open %s", pm->mountpoint);
return NULL;
}
ret = fstat(fd, &st);
ret = fstat(mnt_fd, &st);
if (ret < 0) {
pr_perror("fstat(%s) failed", path);
close(fd);
return NULL;
goto err;
}
if (st.st_dev != pm->s_dev) {
pr_err("The file system %#x %s %s is inaccessible\n",
pm->s_dev, pm->fstype->name, pm->mountpoint);
close(fd);
return NULL;
goto err;
}
fdir = fdopendir(fd);
fdir = fdopendir(mnt_fd);
if (fdir == NULL) {
close(fd);
pr_perror("Can't open %s", pm->mountpoint);
return NULL;
goto err;
}
return fdir;
err:
close(mnt_fd);
return NULL;
}
static int close_mountpoint(DIR *dfd)
@ -249,6 +250,73 @@ static int close_mountpoint(DIR *dfd)
return 0;
}
static DIR *open_mountpoint(struct mount_info *pm)
{
int fd = -1, ns_old = -1;
char buf[PATH_MAX];
char mnt_path[] = "/tmp/cr-tmpfs.XXXXXX";
/*
* If a mount doesn't have children, we can open a mount point,
* otherwise we need to create a "private" copy.
*/
if (list_empty(&pm->children))
return __open_mountpoint(pm, -1);
pr_info("Something is mounted on top of %s\n", pm->mountpoint);
/*
* To create a "private" copy, the target mount is bind-mounted
* in a temporary place w/o MS_REC (non-recursively).
* A mount point can't be bind-mounted in criu's namespace, it will be
* mounted in a target namespace. The sequence of actions is
* mkdtemp, setns(tgt), mount, open, detach, setns(old).
*/
if (switch_ns(root_item->pid.real, &mnt_ns_desc, &ns_old) < 0)
return NULL;
if (mkdtemp(mnt_path) == NULL) {
pr_perror("Can't create a temporary directory");
goto out;
}
snprintf(buf, sizeof(buf), "/proc/self/root/%s", pm->mountpoint);
if (mount(buf, mnt_path, NULL, MS_BIND, NULL)) {
pr_perror("Can't bind-mount %d:%s to %s",
pm->mnt_id, pm->mountpoint, mnt_path);
rmdir(mnt_path);
goto out;
}
fd = open(mnt_path, O_RDONLY | O_DIRECTORY);
if (fd < 0)
pr_perror("Can't open %s\n", mnt_path);
if (umount2(mnt_path, MNT_DETACH)) {
pr_perror("Can't umount %s", mnt_path);
goto out;
}
if (rmdir(mnt_path)) {
pr_perror("Can't remove the directory %s", mnt_path);
goto out;
}
if (fd < 0)
goto out;
if (restore_ns(ns_old, &mnt_ns_desc))
goto out;
return __open_mountpoint(pm, fd);;
out:
if (ns_old >= 0)
restore_ns(ns_old, &mnt_ns_desc);
close_safe(&fd);
return NULL;
}
static int tmpfs_dump(struct mount_info *pm)
{
int ret = -1;