[PATCHv2] Add the proccgroup extension

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Initial version of a crash module which can be used to show which cgroups
is a process member of.  

Signed-off-by: Nikolay Borisov <n.borisov.lkml@xxxxxxxxx>
---

So here is the second version of the proccgroup module. Changes since v1:

 * Now show the full path to the cgroup (limited to 4k long paths).
 * Added support for passing either pid or hex address of task struct, so that 
   cgroup info can be acquired for an arbitrary task 
 * Added support for pre-3.15 kernels
 * Removed leftovers from the echo module

 extensions/proccgroup.c | 278 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 278 insertions(+)
 create mode 100644 extensions/proccgroup.c

diff --git a/extensions/proccgroup.c b/extensions/proccgroup.c
new file mode 100644
index 0000000..aee735b
--- /dev/null
+++ b/extensions/proccgroup.c
@@ -0,0 +1,278 @@
+/*
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * Nikolay Borisov <n.borisov.lkml@xxxxxxxxx>
+ */
+
+#include <stdbool.h>
+#include "defs.h"    
+
+#define MAX_CGROUP_PATH 4096
+
+static void showcgrp(void);
+char *help_proc_cgroups[];
+
+static struct command_table_entry command_table[] = {
+        { "showcg", showcgrp, help_proc_cgroups, 0},
+        { NULL },
+};
+
+
+void __attribute__((constructor))
+proccgroup_init(void)
+{
+
+    if (!MEMBER_EXISTS("task_struct", "cgroups") ||
+        (!MEMBER_EXISTS("cgroup", "kn") && !MEMBER_EXISTS("cgroup", "name")))
+    {
+        fprintf(fp, "Unrecognised or disabled cgroup support\n");
+        return;
+    }
+
+    register_extension(command_table);
+}
+ 
+void __attribute__((destructor))
+proccgroup_finish(void) { }
+
+/* Prepends contents of cgroup_name to buf, using start as a pointer
+ * index into buf
+ */
+static void prepend_string(char *buf, char **start, char *cgroup_name) {
+
+    int len = strlen(cgroup_name);
+    *start -= len;
+
+    if (*start < buf) {
+        error(FATAL, "Cgroup too long to parse\n");
+    }
+    
+    memcpy(*start, cgroup_name, len);
+    
+    if (--*start < buf) {
+        error(FATAL, "Cgroup too long to parse\n");
+    }
+    
+    **start = '/';
+}
+
+/* For post-3.15 kernels */
+static void get_cgroup_name_kn(ulong cgroup, char *buf, int buflen)
+{
+    ulong kernfs_node;
+    ulong cgroup_name_ptr;
+    ulong kernfs_parent;
+    bool slash_prepended = false;
+    char cgroup_name[BUFSIZE];
+    char *start = buf + buflen - 1;
+    *start = '\0'; //null terminate the end 
+
+    /* Get cgroup->kn */
+    readmem(cgroup + MEMBER_OFFSET("cgroup", "kn"), KVADDR, &kernfs_node, sizeof(void *),
+            "cgroup->kn", FAULT_ON_ERROR);
+
+    do {
+        /* Get kn->name */
+        readmem(kernfs_node + MEMBER_OFFSET("kernfs_node", "name"), KVADDR, &cgroup_name_ptr, sizeof(void *),
+                "kernfs_node->name", FAULT_ON_ERROR);
+        /* Get kn->parent */
+        readmem(kernfs_node + MEMBER_OFFSET("kernfs_node", "parent"), KVADDR, &kernfs_parent, sizeof(void *),
+                "kernfs_node->parent", FAULT_ON_ERROR);
+
+        if (kernfs_parent != 0) {
+            read_string(cgroup_name_ptr, cgroup_name, BUFSIZE-1);
+            prepend_string(buf, &start, cgroup_name);
+            slash_prepended = true;
+        } else if (!slash_prepended) {
+            if (--start < buf) {
+                error(FATAL, "Cgroup too long to parse\n");
+            }
+            *start = '/';
+        }
+
+        kernfs_node = kernfs_parent;
+
+    } while(kernfs_parent);
+
+    memmove(buf, start, buf + buflen - start);
+}
+
+/* For pre-3.15 kernels */
+static void get_cgroup_name_old(ulong cgroup, char *buf, size_t buflen)
+{
+    ulong cgroup_name_ptr;
+    ulong cgroup_parent_ptr;
+    char cgroup_name[BUFSIZE];
+    char *start = buf + buflen - 1;
+    *start = '\0'; //null terminate the end 
+    bool slash_prepended = false;
+
+    do {
+        /* Get cgroup->name */
+        readmem(cgroup + MEMBER_OFFSET("cgroup", "name"), KVADDR, &cgroup_name_ptr, sizeof(void *),
+                "cgroup->name", FAULT_ON_ERROR);
+        /* Get cgroup->parent */
+        readmem(cgroup + MEMBER_OFFSET("cgroup", "parent"), KVADDR, &cgroup_parent_ptr, sizeof(void *),
+                "cgroup->parent", FAULT_ON_ERROR);
+
+        read_string(cgroup_name_ptr + MEMBER_OFFSET("cgroup_name", "name"), cgroup_name, BUFSIZE-1);
+
+        if (cgroup_parent_ptr) {
+            prepend_string(buf, &start, cgroup_name);
+            slash_prepended = true;
+        } else if (!slash_prepended) {
+            if (--start < buf)
+                break;
+            *start = '/';
+        }
+
+        cgroup = cgroup_parent_ptr;
+
+    } while(cgroup_parent_ptr);
+
+    memmove(buf, start, buf + buflen - start);
+}
+
+static void get_subsys_name(ulong subsys, char *buf, size_t buflen) 
+{
+    ulong subsys_name_ptr;
+    ulong cgroup_subsys_ptr;
+
+    /* Get cgroup->kn */
+    readmem(subsys + MEMBER_OFFSET("cgroup_subsys_state", "ss"), KVADDR, &cgroup_subsys_ptr, sizeof(void *),
+            "cgroup_subsys_state->ss", FAULT_ON_ERROR);
+
+    readmem(cgroup_subsys_ptr + MEMBER_OFFSET("cgroup_subsys", "name"), KVADDR, &subsys_name_ptr, sizeof(void *),
+            "cgroup_subsys->name", FAULT_ON_ERROR);
+    read_string(subsys_name_ptr, buf, buflen-1);
+}
+
+static void get_cgroup_name(ulong cgroup, ulong subsys)
+{
+    char *cgroup_path = GETBUF(MAX_CGROUP_PATH);
+    char subsys_name[BUFSIZE];
+
+    /* Handle the 2 cases of cgroup_name and the kernfs one */
+    if (MEMBER_EXISTS("cgroup", "kn")) {
+        get_cgroup_name_kn(cgroup, cgroup_path, MAX_CGROUP_PATH);
+    } else if (MEMBER_EXISTS("cgroup", "name")) {
+        get_cgroup_name_old(cgroup, cgroup_path, MAX_CGROUP_PATH);
+    }
+
+    get_subsys_name(subsys, subsys_name, BUFSIZE);
+
+    fprintf(fp, "subsys: %-20s cgroup: %s\n", subsys_name, cgroup_path);
+
+    FREEBUF(cgroup_path);
+}
+
+
+void show_proc_cgroups(ulong task_ctx) {
+    int en_subsys_cnt;
+    int i;
+    ulong *cgroup_subsys_arr;
+    ulong subsys_base_ptr;
+	ulong cgroups_subsys_ptr = 0;
+
+
+    /* Get address of task_struct->cgroups */
+    readmem(task_ctx + MEMBER_OFFSET("task_struct", "cgroups"),
+                            KVADDR, &cgroups_subsys_ptr, sizeof(void *),
+                            "task_struct->cgroups", FAULT_ON_ERROR);
+
+    subsys_base_ptr = cgroups_subsys_ptr + MEMBER_OFFSET("css_set", "subsys");
+    en_subsys_cnt = MEMBER_SIZE("css_set", "subsys") / sizeof(void *);
+    cgroup_subsys_arr = (ulong *)GETBUF(en_subsys_cnt * sizeof(ulong));
+
+    /* Get the contents of the css_set->subsys array */
+    readmem(subsys_base_ptr, KVADDR, cgroup_subsys_arr, sizeof(ulong) * en_subsys_cnt,
+               "css_set->subsys", FAULT_ON_ERROR);
+
+    for (i = 0; i < en_subsys_cnt; i++) {
+        ulong cgroup;
+
+        /* Get cgroup_subsys_state -> cgroup */
+        readmem(cgroup_subsys_arr[i] + MEMBER_OFFSET("cgroup_subsys_state", "cgroup"), 
+                KVADDR, &cgroup, sizeof(void *), "cgroup_subsys_state->cgroup", FAULT_ON_ERROR);
+
+        get_cgroup_name(cgroup, cgroup_subsys_arr[i]);
+    }
+
+    FREEBUF(cgroup_subsys_arr);
+}
+
+
+static void showcgrp(void) {
+   
+    ulong value;
+    struct task_context *tc;
+    ulong task_struct_ptr = 0;
+
+    while (args[++optind]) {
+        if (IS_A_NUMBER(args[optind])) {
+                switch (str_to_context(args[optind], &value, &tc))
+                {
+                case STR_PID:
+                    task_struct_ptr = tc->task;
+                    ++optind;
+                    break;
+    
+                case STR_TASK:
+    		        task_struct_ptr = value;
+                    ++optind;
+                    break;
+    
+                case STR_INVALID:
+                    error(FATAL, "invalid task or pid value: %s\n\n",
+                            args[optind]);
+                    break;
+                }
+        } else {
+            if (argcnt > 1)
+                error(FATAL, "invalid task or pid value: %s\n",args[optind]);
+            else
+                break;
+        }
+    }
+
+    if (!task_struct_ptr) {
+        task_struct_ptr = CURRENT_TASK();
+    }
+
+    show_proc_cgroups(task_struct_ptr);
+}
+
+char *help_proc_cgroups[] = {
+        "showcg",
+        "Show which cgroups is a process member of",
+        " [task | pid]",
+
+        " This command prints the cgroup for each subsys that a process is a member of",
+        "\nExample",
+        "  Show the cgroup for the currently active process:\n",
+        "       crash> showcg",
+        "       subsys: cpuset               cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: cpu                  cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: cpuacct              cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: blkio                cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: memory               cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: devices              cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: freezer              cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: net_cls              cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: perf_event           cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: net_prio             cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "       subsys: hugetlb              cgroup: /user.slice/user-1000.slice/session-c1.scope",
+        "\n  Alternatively you can pass either a pid or a task pointer to show the cgroup the",
+        "  respective process is a member of e.g:\n",
+        "       crash> showcg 1064\n   OR",
+        "       crash> showcg ffff880405711b80",
+
+
+
+        NULL
+};
+
+
-- 
2.5.0

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