Re: [libvirt] [PATCH 1 of 2] Add internal cgroup manipulation functions

This patch adds src/cgroup.{c,h} with support for creating and manipulating cgroups. It's quite naive at the moment, but should provide something to work with to move forward with resource controls. All groups created with the internal API are forced under $mount/libvirt/ to keep everything together. The first time a group is created, the libvirt directory is also created, and the settings from the root are inherited. The code scans the mount table to look for the first mount of type cgroup, and assumes that all controllers are mounted there. I think this could/should be updated to prefer a mount with just the controller(s) we want, if there are multiple ones. If you have the cpuset controller enabled, and cpuset.cpus_exclusive is 1, then all cgroups to be created will fail. Since we probably shouldn't blindly set the root to be non-exclusive, we may also want to consider this condition to be "no cgroup support".

+static virCgroupPtr cgroup_get_mount(void) +{ + FILE *mounts; + struct mntent entry; + char buf[512]; + virCgroupPtr root = NULL; + + root = calloc(1, sizeof(*root)); + if (root == NULL) + return NULL;

+ + mounts = fopen("/proc/mounts", "r"); + if (mounts == NULL) { + DEBUG0("Unable to open /proc/mounts: %m"); + goto err; + } + + while (getmntent_r(mounts, &entry, buf, sizeof(buf)) != NULL) { + if (STREQ(entry.mnt_type, "cgroup")) { + root->path = strdup(entry.mnt_dir); + break; + } + } + + if (root->path == NULL) { + DEBUG0("Did not find cgroup mount"); + goto err; + } + + fclose(mounts); + + return root; +err: + virCgroupFree(&root); + + return NULL; +} + +int virCgroupHaveSupport(void) +{ + virCgroupPtr root; + + root = cgroup_get_mount(); + if (root == NULL) + return -1; + + virCgroupFree(&root); + + return 0; +} + +static int cgroup_path_of(const char *grppath, + const char *key, + char **path) +{ + virCgroupPtr root; + int rc = 0; + + root = cgroup_get_mount(); + if (root == NULL) { + rc = -ENOTDIR; + goto out; + } + + if (asprintf(path, "%s/%s/%s", root->path, grppath, key) == -1) + rc = -ENOMEM; +out: + virCgroupFree(&root); + + return rc; +} + +int virCgroupSetValueStr(virCgroupPtr group, + const char *key, + const char *value) +{ + int fd = -1; + int rc = 0; + char *keypath = NULL; + + rc = cgroup_path_of(group->path, key, &keypath); + if (rc != 0) + return rc; + + fd = open(keypath, O_WRONLY); + if (fd < 0) { + DEBUG("Unable to open %s: %m", keypath); + rc = -ENOENT; + goto out; + } + + DEBUG("Writing '%s' to '%s'", value, keypath); + + rc = safewrite(fd, value, strlen(value)); + if (rc < 0) { + DEBUG("Failed to write value '%s': %m", value); + rc = -errno; + goto out; + } else if (rc != strlen(value)) { + DEBUG("Short write of value '%s'", value); + rc = -ENOSPC; + goto out; + } + + rc = 0; +out: + free(keypath); + close(fd); + + return rc; +} + +int virCgroupSetValueU64(virCgroupPtr group, + const char *key, + uint64_t value) +{ + char *strval = NULL; + int rc; + + if (asprintf(&strval, "%" PRIu64, value) == -1) + return -ENOMEM; + + rc = virCgroupSetValueStr(group, key, strval); + + free(strval);

+ *root = calloc(1, sizeof(**root));

+ if (*root == NULL) { + rc = -ENOMEM; + goto out; + } + + (*root)->path = strdup("libvirt"); + if ((*root)->path == NULL) { + rc = -ENOMEM; + goto out; + } + + rc = cgroup_path_of(".", (*root)->path, &grppath); + if (rc != 0) + goto out; + + if (access(grppath, F_OK) != 0) { + if (mkdir(grppath, 0655) != 0) + rc = -errno; + else + rc = cgroup_inherit(&_root, *root); + } +out: + if (rc != 0) + virCgroupFree(root); + free(grppath); + + return rc; +}