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    Subject[PATCH v7 04/14] firmware_loader: document firmware_sysfs_fallback()
    Date
    This also sets the expecations for future fallback interfaces, even
    if they are not exported.

    Reviewed-by: Kees Cook <keescook@chromium.org>
    Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
    ---
    drivers/base/firmware_loader/fallback.c | 20 ++++++++++++++++++++
    1 file changed, 20 insertions(+)

    diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
    index 3db9e0f225ac..9169e7b9800c 100644
    --- a/drivers/base/firmware_loader/fallback.c
    +++ b/drivers/base/firmware_loader/fallback.c
    @@ -662,6 +662,26 @@ static bool fw_run_sysfs_fallback(enum fw_opt opt_flags)
    return fw_force_sysfs_fallback(opt_flags);
    }

    +/**
    + * firmware_fallback_sysfs() - use the fallback mechanism to find firmware
    + * @fw: pointer to firmware image
    + * @name: name of firmware file to look for
    + * @device: device for which firmware is being loaded
    + * @opt_flags: options to control firmware loading behaviour
    + * @ret: return value from direct lookup which triggered the fallback mechanism
    + *
    + * This function is called if direct lookup for the firmware failed, it enables
    + * a fallback mechanism through userspace by exposing a sysfs loading
    + * interface. Userspace is in charge of loading the firmware through the syfs
    + * loading interface. This syfs fallback mechanism may be disabled completely
    + * on a system by setting the proc sysctl value ignore_sysfs_fallback to true.
    + * If this false we check if the internal API caller set the @FW_OPT_NOFALLBACK
    + * flag, if so it would also disable the fallback mechanism. A system may want
    + * to enfoce the sysfs fallback mechanism at all times, it can do this by
    + * setting ignore_sysfs_fallback to false and force_sysfs_fallback to true.
    + * Enabling force_sysfs_fallback is functionally equivalent to build a kernel
    + * with CONFIG_FW_LOADER_USER_HELPER_FALLBACK.
    + **/
    int firmware_fallback_sysfs(struct firmware *fw, const char *name,
    struct device *device,
    enum fw_opt opt_flags,
    --
    2.17.0
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