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     firmware_register, firmware_unregister, firmware_get, firmware_put —
     firmware image loading and management


     #include <sys/param.h>
     #include <sys/systm.h>
     #include <sys/linker.h>
     #include <sys/firmware.h>

     struct firmware {
             const char      *name;          /* system-wide name */
             const void      *data;          /* location of image */
             size_t          datasize;       /* size of image in bytes */
             unsigned int    version;        /* version of the image */

     const struct firmware *
     firmware_register(const char *imagename, const void *data,
         size_t datasize, unsigned int version,
         const struct firmware *parent);

     firmware_unregister(const char *imagename);

     const struct firmware *
     firmware_get(const char *imagename);

     firmware_put(const struct firmware *fp, int flags);


     The firmware abstraction provides a convenient interface for loading
     firmware images into the kernel, and for accessing such images from
     kernel components.

     A firmware image (or image for brevity) is an opaque block of data
     residing in kernel memory.  It is associated to a unique imagename which
     constitutes a search key, and to an integer version number, which is also
     an opaque piece of information for the firmware subsystem.

     An image is registered with the firmware subsystem by calling the
     function firmware_register(), and unregistered by calling
     firmware_unregister().  These functions are usually (but not exclusively)
     called by specially crafted kernel modules that contain the firmware
     image.  The modules can be statically compiled in the kernel, or loaded
     by /boot/loader, manually at runtime, or on demand by the firmware

     Clients of the firmware subsystem can request access to a given image by
     calling the function firmware_get() with the imagename they want as an
     argument. If a matching image is not already registered, the firmware
     subsystem will try to load it using the mechanisms specified below
     (typically, a kernel module with the same name as the image).


     The kernel firmware API is made of the following functions:

     firmware_register() registers with the kernel an image of size datasize
     located at address data, under the name imagename.

     The function returns NULL on error (e.g. because an image with the same
     name already exists, or the image table is full), or a const struct
     firmware * pointer to the image requested.

     firmware_unregister() tries to unregister the firmware image imagename
     from the system. The function is successful and returns 0 if there are no
     pending references to the image, otherwise it does not unregister the
     image and returns EBUSY.

     firmware_get() returns the requested firmware image.  If the image is not
     yet registered with the system, the function tries to load it.  This
     involves the linker subsystem and disk access, so firmware_get() must not
     be called with any locks (except for Giant).  Note also that if the
     firmware image is loaded from a filesystem it must already be mounted.
     In particular this means that it may be necessary to defer requests from
     a driver attach method unless it is known the root filesystem is already

     On success, firmware_get() returns a pointer to the image description and
     increases the reference count for this image. On failure, the function
     returns NULL.

     firmware_put() drops a reference to a firmware image.  The flags argument
     may be set to FIRMWARE_UNLOAD to indicate that firmware_put is free to
     reclaim resources associated with the firmware image if this is the last
     reference.  By default a firmware image will be deferred to a
     taskqueue(9) thread so the call may be done while holding a lock.  In
     certain cases, such as on driver detach, this cannot be allowed.


     As mentioned before, any component of the system can register firmware
     images at any time by simply calling firmware_register().

     This is typically done when a module containing a firmware image is given
     control, whether compiled in, or preloaded by /boot/loader, or manually
     loaded with kldload(8).  However, a system can implement additional
     mechanisms to bring these images in memory before calling

     When firmware_get() does not find the requested image, it tries to load
     it using one of the available loading mechanisms.  At the moment, there
     is only one, namely Loadable kernel modules:

     A firmware image named foo is looked up by trying to load the module
     named foo.ko, using the facilities described in kld(4).  In particular,
     images are looked up in the directories specified by the sysctl variable
     kern.module_path which on most systems defaults to

     Note that in case a module contains multiple images, the caller should
     first request a firmware_get() for the first image contained in the
     module, followed by requests for the other images.


     A firmware module is built by embedding the firmware image into a
     suitable loadable kernel module that calls firmware_register() on
     loading, and firmware_unregister() on unloading.

     Various system scripts and makefiles let you build a module by simply
     writing a Makefile with the following entries:

             KMOD=   imagename
             FIRMWS= image_file:imagename[:version]
             .include <>

     where KMOD is the basename of the module; FIRMWS is a list of colon-
     separated tuples indicating the image_file's to be embedded in the
     module, the imagename and version of each firmware image.

     If you need to embed firmware images into a system, you should write
     appropriate entries in the <files.arch> file, e.g. this example is from

     ixp425_npe_fw.c                         optional npe_fw                 \
             compile-with    "${AWK} -f $S/tools/fw_stub.awk                 \
                             IxNpeMicrocode.dat:npe_fw -mnpe -c${.TARGET}"   \
             no-implicit-rule before-depend local                            \
             clean           "ixp425_npe_fw.c"
     # NB: ld encodes the path in the binary symbols generated for the
     #     firmware image so link the file to the object directory to
     #     get known values for reference in the _fw.c file.
     IxNpeMicrocode.fwo  optional npe_fw                                     \
             dependency      "IxNpeMicrocode.dat"                            \
             compile-with    "${LD} -b binary -d -warn-common                \
                                 -r -d -o ${.TARGET} IxNpeMicrocode.dat"     \
             no-implicit-rule                                                \
             clean           "IxNpeMicrocode.fwo"
     IxNpeMicrocode.dat                      optional npe_fw                 \
             dependency      ".PHONY"                                        \
             compile-with    "uudecode < $S/contrib/dev/npe/IxNpeMicrocode.dat.uu" \
             no-obj no-implicit-rule                                         \
             clean           "IxNpeMicrocode.dat"

     Note that generating the firmware modules in this way requires the
     availability of the following tools: awk, Make, the compiler and the


     module(9), kld(4)



     The firmware system was introduced in FreeBSD 6.1.


     This manual page was written by Max Laier ⟨⟩.