Re: [PATCH] Fix failure of "dev -d|-D" options on Linux 6.4 and later kernels

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Thank you for the fix, Kazu.
On Tue, May 16, 2023 at 8:27 AM HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx> wrote:
Kernel commit 2df418cf4b72 ("driver core: class: remove subsystem
private pointer from struct class"), which is contained in Linux 6.4 and
later kernels, removed the class.p member for struct subsys_private.  As
a result, the "dev -d|-D" options fail with the following error.

  dev: invalid structure member offset: class_p
       FILE: dev.c  LINE: 4689  FUNCTION: init_iter()

Search the class_kset list for the subsys_private of block class to fix
this.

As a preparation, introduce get_subsys_private() function, which is
abstracted from the same search procedure in init_memory_block().

 
Looks good to me. So: Ack

Thanks.
Lianbo

Signed-off-by: Kazuhito Hagio <k-hagio-ab@xxxxxxx>
---
 defs.h   |  1 +
 dev.c    | 20 +++++++++++++++++---
 memory.c | 35 +++--------------------------------
 tools.c  | 43 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 64 insertions(+), 35 deletions(-)

diff --git a/defs.h b/defs.h
index 211fc9d55d33..21cc760444d1 100644
--- a/defs.h
+++ b/defs.h
@@ -5521,6 +5521,7 @@ struct rb_node *rb_left(struct rb_node *, struct rb_node *);
 struct rb_node *rb_next(struct rb_node *);
 struct rb_node *rb_last(struct rb_root *);
 long percpu_counter_sum_positive(ulong fbc);
+ulong get_subsys_private(char *, char *);

 /*
  *  symbols.c
diff --git a/dev.c b/dev.c
index 75d30bd022a1..9d38aef9b3db 100644
--- a/dev.c
+++ b/dev.c
@@ -4686,9 +4686,16 @@ init_iter(struct iter *i)
                } else {
                        /* kernel version > 2.6.27, klist */
                        unsigned long class_private_addr;
-                       readmem(block_class_addr + OFFSET(class_p), KVADDR,
-                               &class_private_addr, sizeof(class_private_addr),
-                               "class.p", FAULT_ON_ERROR);
+
+                       if (INVALID_MEMBER(class_p)) /* kernel version >= 6.4 */
+                               class_private_addr = get_subsys_private("class_kset", "block");
+                       else
+                               readmem(block_class_addr + OFFSET(class_p), KVADDR,
+                                       &class_private_addr, sizeof(class_private_addr),
+                                       "class.p", FAULT_ON_ERROR);
+
+                       if (!class_private_addr)
+                               error(FATAL, "cannot determine subsys_private for block.\n");

                        if (VALID_STRUCT(class_private)) {
                                /* 2.6.27 < kernel version <= 2.6.37-rc2 */
@@ -4823,6 +4830,13 @@ void diskio_init(void)
        if (INVALID_MEMBER(class_devices))
                MEMBER_OFFSET_INIT(class_devices, "class", "devices");
        MEMBER_OFFSET_INIT(class_p, "class", "p");
+       if (INVALID_MEMBER(class_p)) {
+               MEMBER_OFFSET_INIT(kset_list, "kset", "list");
+               MEMBER_OFFSET_INIT(kset_kobj, "kset", "kobj");
+               MEMBER_OFFSET_INIT(kobject_name, "kobject", "name");
+               MEMBER_OFFSET_INIT(kobject_entry, "kobject", "entry");
+               MEMBER_OFFSET_INIT(subsys_private_subsys, "subsys_private", "subsys");
+       }
        MEMBER_OFFSET_INIT(class_private_devices, "class_private",
                "class_devices");
        MEMBER_OFFSET_INIT(device_knode_class, "device", "knode_class");
diff --git a/memory.c b/memory.c
index 0568f18eb9b7..953fc380c03c 100644
--- a/memory.c
+++ b/memory.c
@@ -17865,38 +17865,9 @@ init_memory_block(int *klistcnt, ulong **klistbuf)
         * v6.3-rc1
         * d2bf38c088e0 driver core: remove private pointer from struct bus_type
         */
-       if (INVALID_MEMBER(bus_type_p)) {
-               int i, cnt;
-               char buf[32];
-               ulong bus_kset, list, name;
-
-               BZERO(ld, sizeof(struct list_data));
-
-               get_symbol_data("bus_kset", sizeof(ulong), &bus_kset);
-               readmem(bus_kset + OFFSET(kset_list), KVADDR, &list,
-                       sizeof(ulong), "bus_kset.list", FAULT_ON_ERROR);
-
-               ld->flags |= LIST_ALLOCATE;
-               ld->start = list;
-               ld->end = bus_kset + OFFSET(kset_list);
-               ld->list_head_offset = OFFSET(kobject_entry);
-
-               cnt = do_list(ld);
-               for (i = 0; i < cnt; i++) {
-                       readmem(ld->list_ptr[i] + OFFSET(kobject_name), KVADDR, &name,
-                               sizeof(ulong), "kobject.name", FAULT_ON_ERROR);
-                       read_string(name, buf, sizeof(buf)-1);
-                       if (CRASHDEBUG(1))
-                               fprintf(fp, "kobject: %lx name: %s\n", ld->list_ptr[i], buf);
-                       if (STREQ(buf, "memory")) {
-                               /* entry is subsys_private.subsys.kobj. See bus_to_subsys(). */
-                               private = ld->list_ptr[i] - OFFSET(kset_kobj)
-                                               - OFFSET(subsys_private_subsys);
-                               break;
-                       }
-               }
-               FREEBUF(ld->list_ptr);
-       } else {
+       if (INVALID_MEMBER(bus_type_p))
+               private = get_subsys_private("bus_kset", "memory");
+       else {
                ulong memory_subsys = symbol_value("memory_subsys");
                readmem(memory_subsys + OFFSET(bus_type_p), KVADDR, &private,
                        sizeof(void *), "memory_subsys.private", FAULT_ON_ERROR);
diff --git a/tools.c b/tools.c
index c2cfa7e280bc..392a79707e61 100644
--- a/tools.c
+++ b/tools.c
@@ -6963,3 +6963,46 @@ percpu_counter_sum_positive(ulong fbc)

        return (ret < 0) ? 0 : ret;
 }
+
+ulong
+get_subsys_private(char *kset_name, char *target_name)
+{
+       ulong kset_addr, kset_list, name_addr, private = 0;
+       struct list_data list_data, *ld;
+       char buf[32];
+       int i, cnt;
+
+       if (!symbol_exists(kset_name))
+               return 0;
+
+       ld = &list_data;
+       BZERO(ld, sizeof(struct list_data));
+
+       get_symbol_data(kset_name, sizeof(ulong), &kset_addr);
+       readmem(kset_addr + OFFSET(kset_list), KVADDR, &kset_list,
+               sizeof(ulong), "kset.list", FAULT_ON_ERROR);
+
+       ld->flags |= LIST_ALLOCATE;
+       ld->start = kset_list;
+       ld->end = kset_addr + OFFSET(kset_list);
+       ld->list_head_offset = OFFSET(kobject_entry);
+
+       cnt = do_list(ld);
+
+       for (i = 0; i < cnt; i++) {
+               readmem(ld->list_ptr[i] + OFFSET(kobject_name), KVADDR, &name_addr,
+                       sizeof(ulong), "kobject.name", FAULT_ON_ERROR);
+               read_string(name_addr, buf, sizeof(buf)-1);
+               if (CRASHDEBUG(1))
+                       fprintf(fp, "kobject: %lx name: %s\n", ld->list_ptr[i], buf);
+               if (STREQ(buf, target_name)) {
+                       /* entry is subsys_private.subsys.kobj. See bus_to_subsys(). */
+                       private = ld->list_ptr[i] - OFFSET(kset_kobj)
+                                       - OFFSET(subsys_private_subsys);
+                       break;
+               }
+       }
+       FREEBUF(ld->list_ptr);
+
+       return private;
+}
--
2.31.1

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