Message-ID: <AANLkTi=e4DMSwpMn0=cV1B1J-=GP=SOGA2qADtUTCQyZ@mail.gmail.com>
Date:	Thu, 17 Feb 2011 13:42:45 -0800
From:	Tim Hockin <thockin@...gle.com>
To:	Mike Waychison <mikew@...gle.com>
Cc:	Greg KH <greg@...ah.com>, Olof Johansson <olofj@...omium.org>,
	Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Robert Lippert <rlippert@...gle.com>,
	Jon Mayer <jonmayer@...gle.com>,
	Duncan Laurie <dlaurie@...gle.com>,
	Aaron Durbin <adurbin@...gle.com>,
	linux-kernel@...r.kernel.org,
	David Hendrix <dhendrix@...omium.org>,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v1 2/5] firmware: Basic dmi-sysfs support

On Thu, Feb 17, 2011 at 1:28 PM, Mike Waychison <mikew@...gle.com> wrote:
> Introduce a new module "dmi-sysfs" that exports the broken out entries
> of the DMI table through sysfs.
>
> Entries are enumerated via dmi_walk() on module load, and are populated
> as kobjects rooted at /sys/firmware/dmi/entries.
>
> Entries are named "<type>-<instance>", where:
>   <type>       : is the type of the entry, and
>   <instance>   : is the ordinal count within the DMI table of that
>                  entry type.  This instance is used in lieu the DMI
>                  entry's handle as no assurances are made by the kernel
>                  that handles are unique.
>
> All entries export the following attributes:
>   length       : The length of the formatted portion of the entry
>   handle       : The handle given to this entry by the firmware
>   raw          : The raw bytes of the entire entry, including the
>                  formatted portion, the unformatted (strings) portion,
>                  and the two terminating nul characters.

Is it worth dropping another file here for type (and maybe one for
ordinal)?  I know they are in the dir name, but something nags at me
that they would be useful here.

>
> Entries in dmi-sysfs are kobject backed members called "struct
> dmi_sysfs_entry" and belong to dmi_kset.  They are threaded through
> entry_list (protected by entry_list_lock) so that we can find them at
> cleanup time.
>
> Signed-off-by: Mike Waychison <mikew@...gle.com>
> ---
>  drivers/firmware/Kconfig     |   11 +
>  drivers/firmware/Makefile    |    1
>  drivers/firmware/dmi-sysfs.c |  362 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 374 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/firmware/dmi-sysfs.c
>
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index e710424..959175d 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -113,6 +113,17 @@ config DMIID
>          information from userspace through /sys/class/dmi/id/ or if you want
>          DMI-based module auto-loading.
>
> +config DMI_SYSFS
> +       tristate "DMI table support in sysfs"
> +       depends on SYSFS && DMI
> +       default X86
> +       help
> +         Say Y or M here to enable the exporting of the raw DMI table
> +         data via sysfs.  This is useful for consuming the data without
> +         requiring any access to /dev/mem at all.  Tables are found
> +         under /sys/firmware/dmi when this option is enabled and
> +         loaded.
> +
>  config ISCSI_IBFT_FIND
>        bool "iSCSI Boot Firmware Table Attributes"
>        depends on X86
> diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
> index 1c3c173..20c17fc 100644
> --- a/drivers/firmware/Makefile
> +++ b/drivers/firmware/Makefile
> @@ -2,6 +2,7 @@
>  # Makefile for the linux kernel.
>  #
>  obj-$(CONFIG_DMI)              += dmi_scan.o
> +obj-$(CONFIG_DMI_SYSFS)                += dmi-sysfs.o
>  obj-$(CONFIG_EDD)              += edd.o
>  obj-$(CONFIG_EFI_VARS)         += efivars.o
>  obj-$(CONFIG_EFI_PCDP)         += pcdp.o
> diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
> new file mode 100644
> index 0000000..adcd604
> --- /dev/null
> +++ b/drivers/firmware/dmi-sysfs.c
> @@ -0,0 +1,362 @@
> +/*
> + * dmi-sysfs.c
> + *
> + * This module exports the DMI tables read-only to userspace through the
> + * sysfs file system.
> + *
> + * Data is currently found below
> + *    /sys/firmware/dmi/...
> + *
> + * DMI attributes are presented in attribute files with names
> + * formatted using %d-%d, so that the first integer indicates the
> + * structure type (0-255), and the second field is the instance of that
> + * entry.
> + *
> + * Copyright 2010 Google, Inc.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <linux/kobject.h>
> +#include <linux/dmi.h>
> +#include <linux/capability.h>
> +#include <linux/slab.h>
> +#include <linux/list.h>
> +#include <linux/io.h>
> +
> +#define MAX_ENTRY_TYPE 255 /* Most of these aren't used, but we consider
> +                             the top entry type is only 8 bits */
> +
> +struct dmi_sysfs_entry {
> +       struct dmi_header dh;
> +       struct kobject kobj;
> +       int instance;
> +       struct list_head list;
> +};
> +
> +/*
> + * Global list of dmi_sysfs_entry.  Even though this should only be
> + * manipulated at setup and teardown, the lazy nature of the kobject
> + * system means we get lazy removes.
> + */
> +static LIST_HEAD(entry_list);
> +static DEFINE_SPINLOCK(entry_list_lock);
> +
> +/* dmi_sysfs_attribute - Top level attribute. used by all entries. */
> +struct dmi_sysfs_attribute {
> +       struct attribute attr;
> +       ssize_t (*show)(struct dmi_sysfs_entry *entry, char *buf);
> +};
> +
> +#define DMI_SYSFS_ATTR(_entry, _name) \
> +struct dmi_sysfs_attribute dmi_sysfs_attr_##_entry##_##_name = { \
> +       .attr = {.name = __stringify(_name), .mode = 0400}, \
> +       .show = dmi_sysfs_##_entry##_##_name, \
> +}
> +
> +/*
> + * dmi_sysfs_mapped_attribute - Attribute where we require the entry be
> + * mapped in.  Use in conjunction with dmi_sysfs_specialize_attr_ops.
> + */
> +struct dmi_sysfs_mapped_attribute {
> +       struct attribute attr;
> +       ssize_t (*show)(struct dmi_sysfs_entry *entry,
> +                       const struct dmi_header *dh,
> +                       char *buf);
> +};
> +
> +#define DMI_SYSFS_MAPPED_ATTR(_entry, _name) \
> +struct dmi_sysfs_mapped_attribute dmi_sysfs_attr_##_entry##_##_name = { \
> +       .attr = {.name = __stringify(_name), .mode = 0400}, \
> +       .show = dmi_sysfs_##_entry##_##_name, \
> +}
> +
> +/*************************************************
> + * Generic DMI entry support.
> + *************************************************/
> +
> +static struct dmi_sysfs_entry *to_entry(struct kobject *kobj)
> +{
> +       return container_of(kobj, struct dmi_sysfs_entry, kobj);
> +}
> +
> +static struct dmi_sysfs_attribute *to_attr(struct attribute *attr)
> +{
> +       return container_of(attr, struct dmi_sysfs_attribute, attr);
> +}
> +
> +static ssize_t dmi_sysfs_attr_show(struct kobject *kobj,
> +                                  struct attribute *_attr, char *buf)
> +{
> +       struct dmi_sysfs_entry *entry = to_entry(kobj);
> +       struct dmi_sysfs_attribute *attr = to_attr(_attr);
> +
> +       /* DMI stuff is only ever admin visible */
> +       if (!capable(CAP_SYS_ADMIN))
> +               return -EACCES;
> +
> +       return attr->show(entry, buf);
> +}
> +
> +static const struct sysfs_ops dmi_sysfs_attr_ops = {
> +       .show = dmi_sysfs_attr_show,
> +};
> +
> +typedef ssize_t (*dmi_callback)(struct dmi_sysfs_entry *,
> +                               const struct dmi_header *dh, void *);
> +
> +struct find_dmi_data {
> +       struct dmi_sysfs_entry  *entry;
> +       dmi_callback            callback;
> +       void                    *private;
> +       int                     instance_countdown;
> +       ssize_t                 ret;
> +};
> +
> +static void find_dmi_entry_helper(const struct dmi_header *dh,
> +                                 void *_data)
> +{
> +       struct find_dmi_data *data = _data;
> +       struct dmi_sysfs_entry *entry = data->entry;
> +
> +       /* Is this the entry we want? */
> +       if (dh->type != entry->dh.type)
> +               return;
> +
> +       if (data->instance_countdown != 0) {
> +               /* try the next instance? */
> +               data->instance_countdown--;
> +               return;
> +       }
> +
> +       /* Found the entry */
> +       data->ret = data->callback(entry, dh, data->private);
> +}
> +
> +/* State for passing the read parameters through dmi_find_entry() */
> +struct dmi_read_state {
> +       char *buf;
> +       loff_t pos;
> +       size_t count;
> +};
> +
> +static ssize_t find_dmi_entry(struct dmi_sysfs_entry *entry,
> +                             dmi_callback callback, void *private)
> +{
> +       struct find_dmi_data data = {
> +               .entry = entry,
> +               .callback = callback,
> +               .private = private,
> +               .instance_countdown = entry->instance,
> +               .ret = -EIO,  /* To signal the entry disappeared */
> +       };
> +       int ret;
> +
> +       ret = dmi_walk(find_dmi_entry_helper, &data);
> +       /* This shouldn't happen, but just in case. */
> +       if (ret)
> +               return -EINVAL;
> +       return data.ret;
> +}
> +
> +/*
> + * Calculate and return the byte length of the dmi entry identified by
> + * dh.  This includes both the formatted portion as well as the
> + * unformatted string space, including the two trailing nul characters.
> + */
> +static size_t dmi_entry_length(const struct dmi_header *dh)
> +{
> +       const char *p = (const char *)dh;
> +
> +       p += dh->length;
> +
> +       while (p[0] || p[1])
> +               p++;
> +
> +       return 2 + p - (const char *)dh;
> +}
> +
> +/*************************************************
> + * Generic DMI entry support.
> + *************************************************/
> +
> +static ssize_t dmi_sysfs_entry_length(struct dmi_sysfs_entry *entry, char *buf)
> +{
> +       return sprintf(buf, "%d\n", entry->dh.length);
> +}
> +
> +static ssize_t dmi_sysfs_entry_handle(struct dmi_sysfs_entry *entry, char *buf)
> +{
> +       return sprintf(buf, "%d\n", entry->dh.handle);
> +}
> +
> +static DMI_SYSFS_ATTR(entry, length);
> +static DMI_SYSFS_ATTR(entry, handle);
> +
> +static struct attribute *dmi_sysfs_entry_attrs[] = {
> +       &dmi_sysfs_attr_entry_length.attr,
> +       &dmi_sysfs_attr_entry_handle.attr,
> +       NULL,
> +};
> +
> +static ssize_t dmi_entry_raw_read_helper(struct dmi_sysfs_entry *entry,
> +                                        const struct dmi_header *dh,
> +                                        void *_state)
> +{
> +       struct dmi_read_state *state = _state;
> +       size_t entry_length;
> +
> +       entry_length = dmi_entry_length(dh);
> +
> +       return memory_read_from_buffer(state->buf, state->count,
> +                                      &state->pos, dh, entry_length);
> +}
> +
> +static ssize_t dmi_entry_raw_read(struct file *filp,
> +                                 struct kobject *kobj,
> +                                 struct bin_attribute *bin_attr,
> +                                 char *buf, loff_t pos, size_t count)
> +{
> +       struct dmi_sysfs_entry *entry = to_entry(kobj);
> +       struct dmi_read_state state = {
> +               .buf = buf,
> +               .pos = pos,
> +               .count = count,
> +       };
> +
> +       return find_dmi_entry(entry, dmi_entry_raw_read_helper, &state);
> +}
> +
> +static const struct bin_attribute dmi_entry_raw_attr = {
> +       .attr = {.name = "raw", .mode = 0400},
> +       .read = dmi_entry_raw_read,
> +};
> +
> +static void dmi_sysfs_entry_release(struct kobject *kobj)
> +{
> +       struct dmi_sysfs_entry *entry = to_entry(kobj);
> +       sysfs_remove_bin_file(&entry->kobj, &dmi_entry_raw_attr);
> +       spin_lock(&entry_list_lock);
> +       list_del(&entry->list);
> +       spin_unlock(&entry_list_lock);
> +       kfree(entry);
> +}
> +
> +static struct kobj_type dmi_sysfs_entry_ktype = {
> +       .release = dmi_sysfs_entry_release,
> +       .sysfs_ops = &dmi_sysfs_attr_ops,
> +       .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 */
> +static int __initdata instance_counts[MAX_ENTRY_TYPE + 1];
> +
> +static void __init dmi_sysfs_register_handle(const struct dmi_header *dh,
> +                                            void *_ret)
> +{
> +       struct dmi_sysfs_entry *entry;
> +       int *ret = _ret;
> +
> +       /* If a previous entry saw an error, short circuit */
> +       if (*ret)
> +               return;
> +
> +       /* Allocate and register a new entry into the entries set */
> +       entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> +       if (!entry) {
> +               *ret = -ENOMEM;
> +               return;
> +       }
> +
> +       /* Set the key */
> +       entry->dh = *dh;
> +       entry->instance = instance_counts[dh->type]++;
> +
> +       entry->kobj.kset = dmi_kset;
> +       *ret = kobject_init_and_add(&entry->kobj, &dmi_sysfs_entry_ktype, NULL,
> +                                   "%d-%d", dh->type, entry->instance);
> +
> +       if (*ret) {
> +               kfree(entry);
> +               return;
> +       }
> +
> +       /* Thread on the global list for cleanup */
> +       spin_lock(&entry_list_lock);
> +       list_add_tail(&entry->list, &entry_list);
> +       spin_unlock(&entry_list_lock);
> +
> +       /* Create the raw binary file to access the entry */
> +       *ret = sysfs_create_bin_file(&entry->kobj, &dmi_entry_raw_attr);
> +       if (*ret)
> +               goto out_err;
> +
> +       return;
> +out_err:
> +       kobject_put(&entry->kobj);
> +       return;
> +}
> +
> +static void cleanup_entry_list(void)
> +{
> +       struct dmi_sysfs_entry *entry, *next;
> +
> +       /* No locks, we are on our way out */
> +       list_for_each_entry_safe(entry, next, &entry_list, list) {
> +               kobject_put(&entry->kobj);
> +       }
> +}
> +
> +static int __init dmi_sysfs_init(void)
> +{
> +       int error = -ENOMEM;
> +       int val;
> +
> +       /* Set up our directory */
> +       dmi_kobj = kobject_create_and_add("dmi", firmware_kobj);
> +       if (!dmi_kobj)
> +               goto err;
> +
> +       dmi_kset = kset_create_and_add("entries", NULL, dmi_kobj);
> +       if (!dmi_kset)
> +               goto err;
> +
> +       val = 0;
> +       error = dmi_walk(dmi_sysfs_register_handle, &val);
> +       if (error)
> +               goto err;
> +       if (val) {
> +               error = val;
> +               goto err;
> +       }
> +
> +       pr_info("dmi-sysfs: loaded.\n");
> +
> +       return 0;
> +err:
> +       cleanup_entry_list();
> +       kset_unregister(dmi_kset);
> +       kobject_put(dmi_kobj);
> +       return error;
> +}
> +
> +/* clean up everything. */
> +static void __exit dmi_sysfs_exit(void)
> +{
> +       pr_info("dmi-sysfs: unloading.\n");
> +       cleanup_entry_list();
> +       kset_unregister(dmi_kset);
> +       kobject_put(dmi_kobj);
> +}
> +
> +module_init(dmi_sysfs_init);
> +module_exit(dmi_sysfs_exit);
> +
> +MODULE_AUTHOR("Google, Inc.");
> +MODULE_DESCRIPTION("DMI sysfs support");
> +MODULE_LICENSE("GPL");
>
>
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