lxc-attach: unify code for attaching a pid to a cgroup

src/lxc/attach.c

@@ -60,10 +60,9 @@ struct lxc_proc_context_info *lxc_proc_get_context_info(pid_t pid)
 	struct lxc_proc_context_info *info = calloc(1, sizeof(*info));
 	FILE *proc_file;
 	char proc_fn[MAXPATHLEN];
-	char *line = NULL, *ptr, *ptr2;
+	char *line = NULL;
 	size_t line_bufsz = 0;
-	int ret, found, l;
-	int i;
+	int ret, found;
 
 	if (!info) {
 		SYSERROR("Could not allocate memory.");
@@ -114,117 +113,14 @@ struct lxc_proc_context_info *lxc_proc_get_context_info(pid_t pid)
 		goto out_error;
 	}
 
-	/* read cgroups */
-	snprintf(proc_fn, MAXPATHLEN, "/proc/%d/cgroup", pid);
-
-	proc_file = fopen(proc_fn, "r");
-	if (!proc_file) {
-		SYSERROR("Could not open %s", proc_fn);
-		goto out_error;
-	}
-
-	/* we don't really know how many cgroup subsystems there are
-	 * mounted, so we go through the whole file twice */
-	i = 0;
-	while (getline(&line, &line_bufsz, proc_file) != -1) {
-		/* we assume that all lines containing at least two colons
-		 * are valid */
-		ptr = strchr(line, ':');
-		if (ptr && strchr(ptr + 1, ':'))
-			i++;
-	}
-
-	rewind(proc_file);
-
-	info->cgroups = calloc(i, sizeof(*(info->cgroups)));
-	info->cgroups_count = i;
-
-	i = 0;
-	while (getline(&line, &line_bufsz, proc_file) != -1 && i < info->cgroups_count) {
-		/* format of the lines is:
-		 * id:subsystems:path, where subsystems are separated by
-		 * commas and each subsystem may also be of the form
-		 * name=xxx if it describes a private named hierarchy
-		 * we will ignore the id in the following */
-		ptr = strchr(line, ':');
-		ptr2 = ptr ? strchr(ptr + 1, ':') : NULL;
-
-		/* ignore invalid lines */
-		if (!ptr || !ptr2) continue;
-
-		l = strlen(ptr2) - 1;
-		if (ptr2[l] == '\n')
-			ptr2[l] = '\0';
-
-		info->cgroups[i].subsystems = strndup(ptr + 1, ptr2 - (ptr + 1));
-		info->cgroups[i].cgroup = strdup(ptr2 + 1);
-
-		i++;
-	}
-
-	free(line);
-	fclose(proc_file);
-
 	return info;
 
 out_error:
-	lxc_proc_free_context_info(info);
+	free(info);
 	free(line);
 	return NULL;
 }
 
-void lxc_proc_free_context_info(struct lxc_proc_context_info *info)
-{
-	if (!info)
-		return;
-
-	if (info->cgroups) {
-		int i;
-		for (i = 0; i < info->cgroups_count; i++) {
-			free(info->cgroups[i].subsystems);
-			free(info->cgroups[i].cgroup);
-		}
-	}
-	free(info->cgroups);
-	free(info);
-}
-
-int lxc_attach_proc_to_cgroups(pid_t pid, struct lxc_proc_context_info *ctx)
-{
-	int i, ret;
-
-	if (!ctx) {
-		ERROR("No valid context supplied when asked to attach "
-		      "process to cgroups.");
-		return -1;
-	}
-
-	for (i = 0; i < ctx->cgroups_count; i++) {
-		char *path;
-
-		/* the kernel should return paths that start with '/' */
-		if (ctx->cgroups[i].cgroup[0] != '/') {
-			ERROR("For cgroup subsystem(s) %s the path '%s' does "
-			      "not start with a '/'",
-			      ctx->cgroups[i].subsystems,
-			      ctx->cgroups[i].cgroup);
-			return -1;
-		}
-
-		/* lxc_cgroup_path_get can process multiple subsystems */
-		ret = lxc_cgroup_path_get(&path, ctx->cgroups[i].subsystems,
-		                          &ctx->cgroups[i].cgroup[1]);
-		if (ret)
-			return -1;
-
-		ret = lxc_cgroup_attach(path, pid);
-		if (ret)
-			return -1;
-	}
-
-	return 0;
-}
-
 int lxc_attach_to_ns(pid_t pid)
 {
 	char path[MAXPATHLEN];

src/lxc/attach.h

@@ -26,22 +26,13 @@
 
 #include <sys/types.h>
 
-struct lxc_proc_cgroup_info {
-	char *subsystems;
-	char *cgroup;
-};
-
 struct lxc_proc_context_info {
 	unsigned long personality;
 	unsigned long long capability_mask;
-	struct lxc_proc_cgroup_info* cgroups;
-	int cgroups_count;
 };
 
 extern struct lxc_proc_context_info *lxc_proc_get_context_info(pid_t pid);
-extern void lxc_proc_free_context_info(struct lxc_proc_context_info *info);
 
-extern int lxc_attach_proc_to_cgroups(pid_t pid, struct lxc_proc_context_info *ctx);
 extern int lxc_attach_to_ns(pid_t other_pid);
 extern int lxc_attach_drop_privs(struct lxc_proc_context_info *ctx);
 

src/lxc/cgroup.c

@@ -53,35 +53,6 @@ enum {
 	CGROUP_CLONE_CHILDREN,
 };
 
-static char *hasmntopt_multiple(struct mntent *mntent, const char *options)
-{
-	const char *ptr = options;
-	const char *ptr2 = strchr(options, ',');
-	char *result;
-
-	while (ptr2 != NULL) {
-		char *option = strndup(ptr, ptr2 - ptr);
-		if (!option) {
-			SYSERROR("Temporary memory allocation error");
-			return NULL;
-		}
-
-		result = hasmntopt(mntent, option);
-		free(option);
-
-		if (!result) {
-			return NULL;
-		}
-
-		ptr = ptr2 + 1;
-		ptr2 = strchr(ptr, ',');
-	}
-
-	/* for multiple mount options, the return value is basically NULL
-	 * or non-NULL, so this should suffice for our purposes */
-	return hasmntopt(mntent, ptr);
-}
-
 /*
  * get_init_cgroup: get the cgroup init is in.
  *  dsg: preallocated buffer to put the output in
@@ -168,7 +139,7 @@ static int get_cgroup_mount(const char *subsystem, char *mnt)
 	while ((mntent = getmntent(file))) {
 		if (strcmp(mntent->mnt_type, "cgroup"))
 			continue;
-		if (subsystem && !hasmntopt_multiple(mntent, subsystem))
+		if (subsystem && !hasmntopt(mntent, subsystem))
 			continue;
 
 		flags = get_cgroup_flags(mntent);
@@ -243,13 +214,20 @@ static int cgroup_enable_clone_children(const char *path)
 	return ret;
 }
 
-int lxc_cgroup_attach(const char *path, pid_t pid)
+static int lxc_one_cgroup_attach(const char *name,
+				 struct mntent *mntent, pid_t pid)
 {
 	FILE *f;
-	char tasks[MAXPATHLEN];
-	int ret = 0;
+	char tasks[MAXPATHLEN], initcgroup[MAXPATHLEN];
+	char *cgmnt = mntent->mnt_dir;
+	int flags, ret = 0;
+
+	flags = get_cgroup_flags(mntent);
 
-	snprintf(tasks, MAXPATHLEN, "%s/tasks", path);
+	snprintf(tasks, MAXPATHLEN, "%s%s%s/%s/tasks", cgmnt,
+	         get_init_cgroup(NULL, mntent, initcgroup),
+	         (flags & CGROUP_NS_CGROUP) ? "" : "/lxc",
+	         name);
 
 	f = fopen(tasks, "w");
 	if (!f) {
@@ -268,6 +246,44 @@ int lxc_cgroup_attach(const char *path, pid_t pid)
 }
 
 /*
+ * for each mounted cgroup, attach a pid to the cgroup for the container
+ */
+int lxc_cgroup_attach(const char *name, pid_t pid)
+{
+	struct mntent *mntent;
+	FILE *file = NULL;
+	int err = -1;
+	int found = 0;
+
+	file = setmntent(MTAB, "r");
+	if (!file) {
+		SYSERROR("failed to open %s", MTAB);
+		return -1;
+	}
+
+	while ((mntent = getmntent(file))) {
+		DEBUG("checking '%s' (%s)", mntent->mnt_dir, mntent->mnt_type);
+
+		if (strcmp(mntent->mnt_type, "cgroup"))
+			continue;
+
+		INFO("[%d] found cgroup mounted at '%s',opts='%s'",
+		     ++found, mntent->mnt_dir, mntent->mnt_opts);
+
+		err = lxc_one_cgroup_attach(name, mntent, pid);
+		if (err)
+			goto out;
+	};
+
+	if (!found)
+		ERROR("No cgroup mounted on the system");
+
+out:
+	endmntent(file);
+	return err;
+}
+
+/*
  * rename cgname, which is under cgparent, to a new name starting
  * with 'cgparent/dead'.  That way cgname can be reused.  Return
  * 0 on success, -1 on failure.
@@ -378,20 +394,13 @@ static int lxc_one_cgroup_create(const char *name,
 		return -1;
 	}
 
-	/* Let's add the pid to the 'tasks' file */
-	if (lxc_cgroup_attach(cgname, pid)) {
-		SYSERROR("failed to attach pid '%d' to '%s'", pid, cgname);
-		rmdir(cgname);
-		return -1;
-	}
-
 	INFO("created cgroup '%s'", cgname);
 
 	return 0;
 }
 
 /*
- * for each mounted cgroup, create a cgroup for the container
+ * for each mounted cgroup, create a cgroup for the container and attach a pid
  */
 int lxc_cgroup_create(const char *name, pid_t pid)
 {
@@ -418,6 +427,10 @@ int lxc_cgroup_create(const char *name, pid_t pid)
 		err = lxc_one_cgroup_create(name, mntent, pid);
 		if (err)
 			goto out;
+
+		err = lxc_one_cgroup_attach(name, mntent, pid);
+		if (err)
+			goto out;
 	};
 
 	if (!found)

src/lxc/cgroup.h

@@ -30,6 +30,6 @@ extern int lxc_cgroup_create(const char *name, pid_t pid);
 extern int lxc_cgroup_destroy(const char *name);
 extern int lxc_cgroup_path_get(char **path, const char *subsystem, const char *name);
 extern int lxc_cgroup_nrtasks(const char *name);
-extern int lxc_cgroup_attach(const char *path, pid_t pid);
+extern int lxc_cgroup_attach(const char *name, pid_t pid);
 extern int lxc_ns_is_mounted(void);
 #endif

src/lxc/lxc_attach.c

@@ -35,7 +35,7 @@
 #include "commands.h"
 #include "arguments.h"
 #include "caps.h"
-#include "attach.h"
+#include "cgroup.h"
 #include "confile.h"
 #include "start.h"
 #include "sync.h"
@@ -150,7 +150,7 @@ int main(int argc, char *argv[])
 		if (lxc_sync_wait_child(handler, LXC_SYNC_CONFIGURE))
 			return -1;
 
-		if (!elevated_privileges && lxc_attach_proc_to_cgroups(pid, init_ctx))
+		if (!elevated_privileges && lxc_cgroup_attach(my_args.name, pid))
 			return -1;
 
 		/* tell the child we are done initializing */