Re: [Patch v3] firmware: dmi-sysfs: add SMBIOS entry point area raw attribute

[Mark Salter]

On Wed, 2015-01-28 at 14:39 +0200, Ivan Khoronzhuk wrote:
> Some utils, like dmidecode and smbios, needs 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. So this patch adds SMBIOS area to
> dmi-sysfs in order to allow utils in question to work correctly with
> dmi sysfs interface.
> 
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>

Sorry for coming in late, here. Why expose the raw header
instead of exposing the pieces as individual files like
the kernel does for the other dmi info? That way the kernel
decodes the header and presents it in an easy to read
format for dmidecode or even a shell script.

> ---
> 
> v1: https://lkml.org/lkml/2015/1/23/643
> v2: https://lkml.org/lkml/2015/1/26/345
> 
> v3..v2:
>   firmware: dmi_scan: add symbol to get SMBIOS entry area
>   firmware: dmi-sysfs: add SMBIOS entry point area attribute
> 	combined in one patch
> 	added SMBIOS information to ABI sysfs-dmi documentaton
> 
> v2..v1:
>   firmware: dmi_scan: add symbol to get SMBIOS entry area
> 	- used additional static var to hold SMBIOS raw table size
> 	- changed format of get_smbios_entry_area symbol
> 	  returned pointer on const smbios table
> 
>   firmware: dmi-sysfs: add SMBIOS entry point area attribute
> 	- adopted to updated get_smbios_entry_area symbol
>   	- removed redundant array to save smbios table
> 
> 
>  Documentation/ABI/testing/sysfs-firmware-dmi | 10 +++++++
>  drivers/firmware/dmi-sysfs.c                 | 42 ++++++++++++++++++++++++++++
>  drivers/firmware/dmi_scan.c                  | 26 +++++++++++++++++
>  include/linux/dmi.h                          |  3 ++
>  4 files changed, 81 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-firmware-dmi b/Documentation/ABI/testing/sysfs-firmware-dmi
> index c78f9ab..3a9ffe8 100644
> --- a/Documentation/ABI/testing/sysfs-firmware-dmi
> +++ b/Documentation/ABI/testing/sysfs-firmware-dmi
> @@ -12,6 +12,16 @@ Description:
>  		cannot ensure that the data as exported to userland is
>  		without error either.
>  
> +		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.
> +		That's why SMBIOS entry point is represented in dmi sysfs
> +		like a raw attribute and is accessible via
> +		/sys/firmware/dmi/smbios_raw_header. The format of SMBIOS
> +		entry point header can be read in SMBIOS specification.
> +
>  		DMI is structured as a large table of entries, where
>  		each entry has a common header indicating the type and
>  		length of the entry, as well as a firmware-provided
> diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
> index e0f1cb3..61b6a38 100644
> --- a/drivers/firmware/dmi-sysfs.c
> +++ b/drivers/firmware/dmi-sysfs.c
> @@ -29,6 +29,8 @@
>  #define MAX_ENTRY_TYPE 255 /* Most of these aren't used, but we consider
>  			      the top entry type is only 8 bits */
>  
> +static const u8 *smbios_raw_header;
> +
>  struct dmi_sysfs_entry {
>  	struct dmi_header dh;
>  	struct kobject kobj;
> @@ -646,9 +648,37 @@ static void cleanup_entry_list(void)
>  	}
>  }
>  
> +static ssize_t smbios_entry_area_raw_read(struct file *filp,
> +					  struct kobject *kobj,
> +					  struct bin_attribute *bin_attr,
> +					  char *buf, loff_t pos, size_t count)
> +{
> +	ssize_t size;
> +
> +	size = bin_attr->size;
> +
> +	if (size > pos)
> +		size -= pos;
> +	else
> +		return 0;
> +
> +	if (count < size)
> +		size = count;
> +
> +	memcpy(buf, &smbios_raw_header[pos], size);
> +
> +	return size;
> +}
> +
> +static struct bin_attribute smbios_raw_area_attr = {
> +	.read = smbios_entry_area_raw_read,
> +	.attr = {.name = "smbios_raw_header", .mode = 0400},
> +};
> +
>  static int __init dmi_sysfs_init(void)
>  {
>  	int error = -ENOMEM;
> +	int size;
>  	int val;
>  
>  	/* Set up our directory */
> @@ -669,6 +699,18 @@ static int __init dmi_sysfs_init(void)
>  		goto err;
>  	}
>  
> +	smbios_raw_header = dmi_get_smbios_entry_area(&size);
> +	if (!smbios_raw_header) {
> +		pr_debug("dmi-sysfs: SMBIOS raw data is not available.\n");
> +		error = -ENODATA;
> +		goto err;
> +	}
> +
> +	/* Create the raw binary file to access the entry area */
> +	smbios_raw_area_attr.size = size;
> +	if (sysfs_create_bin_file(dmi_kobj, &smbios_raw_area_attr))
> +		goto err;
> +
>  	pr_debug("dmi-sysfs: loaded.\n");
>  
>  	return 0;
> diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> index 420c8d8..d94c6b7 100644
> --- a/drivers/firmware/dmi_scan.c
> +++ b/drivers/firmware/dmi_scan.c
> @@ -113,6 +113,8 @@ static void dmi_table(u8 *buf, int len, int num,
>  	}
>  }
>  
> +static unsigned char smbios_header[32];
> +static int smbios_header_size;
>  static phys_addr_t dmi_base;
>  static u16 dmi_len;
>  static u16 dmi_num;
> @@ -474,6 +476,8 @@ 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_header_size = buf[5];
> +		memcpy(smbios_header, buf, smbios_header_size);
>  
>  		/* Some BIOS report weird SMBIOS version, fix that up */
>  		switch (smbios_ver) {
> @@ -505,6 +509,8 @@ static int __init dmi_present(const u8 *buf)
>  				pr_info("SMBIOS %d.%d present.\n",
>  				       dmi_ver >> 8, dmi_ver & 0xFF);
>  			} else {
> +				smbios_header_size = 15;
> +				memcpy(smbios_header, buf, smbios_header_size);
>  				dmi_ver = (buf[14] & 0xF0) << 4 |
>  					   (buf[14] & 0x0F);
>  				pr_info("Legacy DMI %d.%d present.\n",
> @@ -531,6 +537,8 @@ 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_header_size = buf[6];
> +		memcpy(smbios_header, buf, smbios_header_size);
>  
>  		/*
>  		 * The 64-bit SMBIOS 3.0 entry point no longer has a field
> @@ -944,3 +952,21 @@ void dmi_memdev_name(u16 handle, const char **bank, const char **device)
>  	}
>  }
>  EXPORT_SYMBOL_GPL(dmi_memdev_name);
> +
> +/**
> + * dmi_get_smbios_entry_area - copy SMBIOS entry point area to array.
> + * @size - pointer to assign actual size of SMBIOS entry point area.
> + *
> + * returns NULL if table is not available, otherwise returns pointer on
> + * SMBIOS entry point area array.
> + */
> +const u8 *dmi_get_smbios_entry_area(int *size)
> +{
> +	if (!smbios_header_size || !dmi_available)
> +		return NULL;
> +
> +	*size = smbios_header_size;
> +
> +	return smbios_header;
> +}
> +EXPORT_SYMBOL_GPL(dmi_get_smbios_entry_area);
> diff --git a/include/linux/dmi.h b/include/linux/dmi.h
> index f820f0a..8e1a28d 100644
> --- a/include/linux/dmi.h
> +++ b/include/linux/dmi.h
> @@ -109,6 +109,7 @@ extern int dmi_walk(void (*decode)(const struct dmi_header *, void *),
>  	void *private_data);
>  extern bool dmi_match(enum dmi_field f, const char *str);
>  extern void dmi_memdev_name(u16 handle, const char **bank, const char **device);
> +const u8 *dmi_get_smbios_entry_area(int *size);
>  
>  #else
>  
> @@ -140,6 +141,8 @@ static inline void dmi_memdev_name(u16 handle, const char **bank,
>  		const char **device) { }
>  static inline const struct dmi_system_id *
>  	dmi_first_match(const struct dmi_system_id *list) { return NULL; }
> +static inline const u8 *dmi_get_smbios_entry_area(int *size)
> +	{ return NULL; }
>  
>  #endif
>  


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