Re: [Patch 2/3] firmware: dmi_scan: add SBMIOS entry and DMI tables

Jean Delvare
2015-04-16T09:52:52Z

Hi Ivan,

On Thu, 2 Apr 2015 15:57:02 +0300, Ivan Khoronzhuk wrote:
> Some utils, like dmidecode and smbios, need to access SMBIOS entry
> table area in order to get information like SMBIOS version, size, etc.
> Currently it's done via /dev/mem. But for situation when /dev/mem
> usage is disabled, the utils have to use dmi sysfs instead, which
> doesn't represent SMBIOS entry and adds code/delay redundancy when direct
> access for table is needed.
>
> So this patch creates dmi/tables and adds SMBIOS entry point to allow
> utils in question to work correctly without /dev/mem. Also patch adds
> raw dmi table to simplify dmi table processing in user space, as
> proposed by Jean Delvare.
>
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@globallogic.com>
> ---
> .../ABI/testing/sysfs-firmware-dmi-tables | 22 ++++++
> drivers/firmware/dmi-sysfs.c | 11 ++-
> drivers/firmware/dmi_scan.c | 80 ++++++++++++++++++++++
> include/linux/dmi.h | 1 +
> 4 files changed, 107 insertions(+), 7 deletions(-)
> create mode 100644 Documentation/ABI/testing/sysfs-firmware-dmi-tables

First of all: thanks for doing this, it looks mostly good now, and I've
tested it successfully on my own system.

> diff --git a/Documentation/ABI/testing/sysfs-firmware-dmi-tables b/Documentation/ABI/testing/sysfs-firmware-dmi-tables
> new file mode 100644
> index 0000000..f46158c
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-firmware-dmi-tables
> @@ -0,0 +1,22 @@
> +What: /sys/firmware/dmi/tables/
> +Date: April 2015
> +Contact: Ivan Khoronzhuk <ivan.khoronzhuk@globallogic.com>
> +Description:
> + The firmware provides DMI structures as a packed list of
> + data referenced by a SMBIOS table entry point. The SMBIOS
> + entry point contains general information, like SMBIOS
> + version, DMI table size, etc. The structure, content and
> + size of SMBIOS entry point is dependent on SMBIOS version.
> + The format of SMBIOS entry point, equal as DMI structures
> + can be read in SMBIOS specification.

"equal as" sounds strange, I think a simple "and" would be better.

> +
> + The dmi/tables provides raw SMBIOS entry point and DMI tables
> + through sysfs as an alternative to utilities reading them
> + from /dev/mem. The raw SMBIOS entry point and DMI table are
> + presented as raw attributes and are accessible via:

"binary attributes" rather than "raw attributes"? The "raw" nature is
already mentioned earlier in the sentence.

> +
> + /sys/firmware/dmi/tables/smbios_entry_point
> + /sys/firmware/dmi/tables/DMI
> +
> + The complete DMI information can be taken using these two

"obtained" or "decoded" would sound better than "taken" IMHO.

> + tables.
> diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
> index e0f1cb3..8e1a411 100644
> --- a/drivers/firmware/dmi-sysfs.c
> +++ b/drivers/firmware/dmi-sysfs.c
> @@ -566,7 +566,6 @@ static struct kobj_type dmi_sysfs_entry_ktype = {
> .default_attrs = dmi_sysfs_entry_attrs,
> };
>
> -static struct kobject *dmi_kobj;
> static struct kset *dmi_kset;
>
> /* Global count of all instances seen. Only for setup */
> @@ -651,10 +650,11 @@ static int __init dmi_sysfs_init(void)
> int error = -ENOMEM;

This initialization can be moved to the single error path left that
needs it. (I can do it myself in a separate patch if you don't want to
do it here.)

> int val;
>
> - /* Set up our directory */
> - dmi_kobj = kobject_create_and_add("dmi", firmware_kobj);
> - if (!dmi_kobj)
> + if (!dmi_kobj) {
> + pr_err("dmi-sysfs: dmi entry is absent.\n");
> + error = -ENOSYS;
> goto err;
> + }
>
> dmi_kset = kset_create_and_add("entries", NULL, dmi_kobj);
> if (!dmi_kset)
> @@ -675,7 +675,6 @@ static int __init dmi_sysfs_init(void)
> err:
> cleanup_entry_list();
> kset_unregister(dmi_kset);
> - kobject_put(dmi_kobj);
> return error;
> }
>
> @@ -685,8 +684,6 @@ static void __exit dmi_sysfs_exit(void)
> pr_debug("dmi-sysfs: unloading.\n");
> cleanup_entry_list();
> kset_unregister(dmi_kset);
> - kobject_del(dmi_kobj);
> - kobject_put(dmi_kobj);
> }
>
> module_init(dmi_sysfs_init);
> diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> index d3aae09..bb19f8b 100644
> --- a/drivers/firmware/dmi_scan.c
> +++ b/drivers/firmware/dmi_scan.c
> @@ -10,6 +10,9 @@
> #include <asm/dmi.h>
> #include <asm/unaligned.h>
>
> +struct kobject *dmi_kobj;
> +EXPORT_SYMBOL_GPL(dmi_kobj);
> +
> /*
> * DMI stands for "Desktop Management Interface". It is part
> * of and an antecedent to, SMBIOS, which stands for System
> @@ -20,6 +23,9 @@ static const char dmi_empty_string[] = " ";
> static u32 dmi_ver __initdata;
> static u32 dmi_len;
> static u16 dmi_num;
> +static u8 smbios_entry_point[32];
> +static int smbios_entry_point_size;
> +
> /*
> * Catch too early calls to dmi_check_system():
> */
> @@ -118,6 +124,7 @@ static void dmi_decode_table(u8 *buf,
> }
>
> static phys_addr_t dmi_base;
> +static u8 *dmi_table;

This variable is only ever used in a single function (dmi_init). Does
it actually need to be a global variable? I suspect not.

>
> static int __init dmi_walk_early(void (*decode)(const struct dmi_header *,
> void *))
> @@ -476,6 +483,8 @@ static int __init dmi_present(const u8 *buf)
> if (memcmp(buf, "_SM_", 4) == 0 &&
> buf[5] < 32 && dmi_checksum(buf, buf[5])) {
> smbios_ver = get_unaligned_be16(buf + 6);
> + smbios_entry_point_size = buf[5];
> + memcpy(smbios_entry_point, buf, smbios_entry_point_size);
>
> /* Some BIOS report weird SMBIOS version, fix that up */
> switch (smbios_ver) {
> @@ -508,6 +517,9 @@ static int __init dmi_present(const u8 *buf)
> dmi_ver >> 8, dmi_ver & 0xFF,
> (dmi_ver < 0x0300) ? "" : ".x");
> } else {
> + smbios_entry_point_size = 15;
> + memcpy(smbios_entry_point, buf,
> + smbios_entry_point_size);
> dmi_ver = (buf[14] & 0xF0) << 4 |
> (buf[14] & 0x0F);
> pr_info("Legacy DMI %d.%d present.\n",
> @@ -535,6 +547,8 @@ static int __init dmi_smbios3_present(const u8 *buf)
> dmi_ver &= 0xFFFFFF;
> dmi_len = get_unaligned_le32(buf + 12);
> dmi_base = get_unaligned_le64(buf + 16);
> + smbios_entry_point_size = buf[6];
> + memcpy(smbios_entry_point, buf, smbios_entry_point_size);
>
> /*
> * The 64-bit SMBIOS 3.0 entry point no longer has a field
> @@ -638,6 +652,72 @@ void __init dmi_scan_machine(void)
> dmi_initialized = 1;
> }
>
> +static ssize_t raw_table_read(struct file *file, struct kobject *kobj,
> + struct bin_attribute *attr, char *buf,
> + loff_t pos, size_t count)
> +{
> + memcpy(buf, attr->private + pos, count);
> + return count;
> +}
> +
> +static BIN_ATTR(smbios_entry_point, S_IRUSR, raw_table_read, NULL, 0);

This one could be world-readable as it contains no sensitive
information.

> +struct bin_attribute bin_attr_dmi_table =
> + __BIN_ATTR(DMI, S_IRUSR, raw_table_read, NULL, 0);

I do not understand why you don't use BIN_ATTR here too? I tried naming
the attribute bin_attr_DMI and it seems to work just fine, checkpatch
doesn't even complain!

> +
> +static int __init dmi_init(void)
> +{
> + int ret = -ENOMEM;
> + struct kobject *tables_kobj = NULL;
> +
> + if (!dmi_available) {
> + ret = -ENOSYS;
> + goto err;
> + }

This is weird. Can this actually happen?

We currently have two ways to enter this module: dmi_scan_machine(),
which is called by the architecture code, and dmi_init(), which is
called at subsys_initcall time. As far as I can see,
core/arch_initcalls are guaranteed to be always called before
subsys_initcalls. If we can rely on that, the test above is not needed.
If for any reason we can't, that means that dmi_init() should not be a
subsys_initcall, but should instead be called explicitly at the end of
dmi_scan_machine().

> +
> + /* Set up dmi directory at /sys/firmware/dmi */
> + dmi_kobj = kobject_create_and_add("dmi", firmware_kobj);
> + if (!dmi_kobj)
> + goto err;
> +
> + tables_kobj = kobject_create_and_add("tables", dmi_kobj);
> + if (!tables_kobj)
> + goto err;
> +
> + bin_attr_smbios_entry_point.size = smbios_entry_point_size;
> + bin_attr_smbios_entry_point.private = smbios_entry_point;
> + ret = sysfs_create_bin_file(tables_kobj, &bin_attr_smbios_entry_point);
> + if (ret)
> + goto err;
> +
> + dmi_table = dmi_remap(dmi_base, dmi_len);
> + if (!dmi_table)
> + goto err;

At this point "ret" has value 0 so you will take the error path but
return with success. No good. I suggest that you move the call to
dmi_remap before the first call to sysfs_create_bin_file above, so that
"ret" still has value -ENOMEM.

> +
> + bin_attr_dmi_table.size = dmi_len;
> + bin_attr_dmi_table.private = dmi_table;
> + ret = sysfs_create_bin_file(tables_kobj, &bin_attr_dmi_table);
> + if (ret) {
> + dmi_unmap(dmi_table);

Doing this here goes against the logic of having a single error path.
Instead you should have an additional error label before err: and jump
there.

> + goto err;
> + }
> +
> + return 0;
> +err:
> + pr_err("dmi: Firmware registration failed.\n");
> +
> + if (tables_kobj)
> + sysfs_remove_bin_file(tables_kobj,
> + &bin_attr_smbios_entry_point);
> + kobject_del(tables_kobj);
> + kobject_put(tables_kobj);

These last two calls could be moved inside the conditional above. Even
better would be a separate error label so that you know exactly what
needs to be undone.

> + kobject_del(dmi_kobj);
> + kobject_put(dmi_kobj);
> + dmi_kobj = NULL;

I'm wondering, wouldn't it make sense to keep dmi_kobj alive (with an
appropriate comment), so that dmi-sysfs has a chance to load? As it is
now, a bug or some unexpected behavior in this new code could cause a
regression for dmi-sysfs users. Just because I don't like dmi_sysfs
doesn't mean we can break it ;-)

> +
> + return ret;
> +}
> +subsys_initcall(dmi_init);
> +
> /**
> * dmi_set_dump_stack_arch_desc - set arch description for dump_stack()
> *
> diff --git a/include/linux/dmi.h b/include/linux/dmi.h
> index f820f0a..9f55f46 100644
> --- a/include/linux/dmi.h
> +++ b/include/linux/dmi.h
> @@ -93,6 +93,7 @@ struct dmi_dev_onboard {
> int devfn;
> };
>
> +extern struct kobject *dmi_kobj;

struct kobject is defined in <linux/kobject.h> so I think you should
include that file to avoid random build failures in the future.

> extern int dmi_check_system(const struct dmi_system_id *list);
> const struct dmi_system_id *dmi_first_match(const struct dmi_system_id *list);
> extern const char * dmi_get_system_info(int field);

--
Jean Delvare
SUSE L3 Support