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Refactor nsexec.c and add some comments 

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
This commit is contained in:
Qiang Huang 2016-03-28 11:16:12 +08:00
parent f5ad78dc49
commit 3b7e10652b
1 changed files with 57 additions and 51 deletions
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108
libcontainer/nsenter/nsexec.c
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@ -39,6 +39,7 @@ struct nsenter_config {
char *gidmap;
int gidmap_len;
uint8_t is_setgroup;
int consolefd;
};
// list of known message types we want to send to bootstrap program
@ -86,6 +87,8 @@ static int clone_parent(jmp_buf *env, int flags)
ca.env = env;
child = clone(child_func, ca.stack_ptr, CLONE_PARENT | SIGCHLD | flags,
&ca);
// On old kernels, CLONE_PARENT cannot work with CLONE_NEWPID,
// unshare before clone to workaround this.
if (child == -1 && errno == EINVAL) {
if (unshare(flags)) {
pr_perror("Unable to unshare namespaces");
@ -244,7 +247,6 @@ static void start_child(int pipenum, jmp_buf *env, int syncpipe[2],
// update uid_map and gid_map for the child process if they
// were provided
update_process_uidmap(childpid, config->uidmap, config->uidmap_len);
update_process_gidmap(childpid, config->is_setgroup, config->gidmap, config->gidmap_len);
// Send the sync signal to the child
@ -266,16 +268,14 @@ static void start_child(int pipenum, jmp_buf *env, int syncpipe[2],
exit(0);
}
static void process_nl_attributes(int pipenum, char *data, int data_size)
static struct nsenter_config process_nl_attributes(int pipenum, char *data, int data_size)
{
jmp_buf env;
struct nsenter_config config = {0};
struct nlattr *nlattr;
int payload_len;
int start = 0;
int consolefd = -1;
int syncpipe[2] = {-1, -1};
config.consolefd = -1;
while (start < data_size) {
nlattr = (struct nlattr *)(data + start);
start += NLA_HDRLEN;
@ -286,8 +286,8 @@ static void process_nl_attributes(int pipenum, char *data, int data_size)
} else if (nlattr->nla_type == CONSOLE_PATH_ATTR) {
// get the console path before setns because it may
// change mnt namespace
consolefd = open(data + start, O_RDWR);
if (consolefd < 0) {
config.consolefd = open(data + start, O_RDWR);
if (config.consolefd < 0) {
pr_perror("Failed to open console %s",
data + start);
exit(1);
@ -344,14 +344,61 @@ static void process_nl_attributes(int pipenum, char *data, int data_size)
start += NLA_ALIGN(payload_len);
}
return config;
}
void nsexec(void)
{
int pipenum;
// If we don't have init pipe, then just return to the go routine,
// we'll only have init pipe for start or exec
pipenum = get_init_pipe();
if (pipenum == -1) {
return;
}
// Retrieve the netlink header
struct nlmsghdr nl_msg_hdr;
int len;
if ((len = read(pipenum, &nl_msg_hdr, NLMSG_HDRLEN)) != NLMSG_HDRLEN) {
pr_perror("Invalid netlink header length %d", len);
exit(1);
}
if (nl_msg_hdr.nlmsg_type == NLMSG_ERROR) {
pr_perror("Failed to read netlink message");
exit(1);
}
if (nl_msg_hdr.nlmsg_type != INIT_MSG) {
pr_perror("Unexpected msg type %d", nl_msg_hdr.nlmsg_type);
exit(1);
}
// Retrieve data
int nl_total_size = NLMSG_PAYLOAD(&nl_msg_hdr, 0);
char data[nl_total_size];
if ((len = read(pipenum, data, nl_total_size)) != nl_total_size) {
pr_perror("Failed to read netlink payload, %d != %d", len,
nl_total_size);
exit(1);
}
jmp_buf env;
int syncpipe[2] = {-1, -1};
struct nsenter_config config = process_nl_attributes(pipenum,
data, nl_total_size);
// required clone_flags to be passed
if (config.cloneflags == -1) {
pr_perror("Missing clone_flags");
exit(1);
}
// prepare sync pipe between parent and child. We need this to let the
// child
// know that the parent has finished setting up
// child know that the parent has finished setting up
if (pipe(syncpipe) != 0) {
pr_perror("Failed to setup sync pipe between parent and child");
exit(1);
@ -360,6 +407,7 @@ static void process_nl_attributes(int pipenum, char *data, int data_size)
if (setjmp(env) == 1) {
// Child
uint8_t s = 0;
int consolefd = config.consolefd;
// close the writing side of pipe
close(syncpipe[1]);
@ -416,45 +464,3 @@ static void process_nl_attributes(int pipenum, char *data, int data_size)
// Parent
start_child(pipenum, &env, syncpipe, &config);
}
void nsexec(void)
{
int pipenum;
// if we dont have init pipe, then just return to the parent
pipenum = get_init_pipe();
if (pipenum == -1) {
return;
}
// Retrieve the netlink header
struct nlmsghdr nl_msg_hdr;
int len;
if ((len = read(pipenum, &nl_msg_hdr, NLMSG_HDRLEN)) != NLMSG_HDRLEN) {
pr_perror("Invalid netlink header length %d", len);
exit(1);
}
if (nl_msg_hdr.nlmsg_type == NLMSG_ERROR) {
pr_perror("Failed to read netlink message");
exit(1);
}
if (nl_msg_hdr.nlmsg_type != INIT_MSG) {
pr_perror("Unexpected msg type %d", nl_msg_hdr.nlmsg_type);
exit(1);
}
// Retrieve data
int nl_total_size = NLMSG_PAYLOAD(&nl_msg_hdr, 0);
char data[nl_total_size];
if ((len = read(pipenum, data, nl_total_size)) != nl_total_size) {
pr_perror("Failed to read netlink payload, %d != %d", len,
nl_total_size);
exit(1);
}
process_nl_attributes(pipenum, data, nl_total_size);
}