====== How to deblob a kernel patch ======

Sometimes, there are drivers aren't available from official Linux kernels such as specific drivers and device trees for ARM architecture adapted for certain SoCs, however a lot of them contains nonfree drivers or blobs, then is needed deblob them to protect your freedom.

===== What is a blob? =====

A **Blob** is a piece of object code distributed without source, usually firmware to run some device. That firmware is distributed only in object code form, under a nonfree license. 

===== What is deblobbing? =====

**Deblobbing** is the way to remove blobs from the source or patches.

===== deblob-check =====

[[http://www.fsfla.org/svn/fsfla/software/linux-libre/scripts/deblob-check|deblob-check]] is a script written by Alexandre Oliva. It is the easiest way to looking for blobs to remove them from kernel sources and kernel patches.

==== How to use deblob-check to deblob kernel patches? ====

The command to begin deblob a patch is check the sequences that match the blob detector test with **-B**, eg:

<code bash>
./deblob-check  -B name.patch
</code>

Common results could be such as:

<code>
err = request_firmware_direct(&ditem->fw, item->overlay_name, dev);
</code>

and

<code>
#define WL18XX_CONF_FILE_NAME "ti-connectivity/wl18xx-conf.bin"
</code>

In this case, you should check if those references were deblobbed in deblob-x.y of the kernel version that you are using. You can get it at the [[http://www.fsfla.org/svn/fsfla/software/linux-libre/scripts/|Linux-libre scripts page]] (eg. [[http://www.fsfla.org/svn/fsfla/software/linux-libre/scripts/deblob-4.9|4.9-gnu]]).

If those references aren't available in Linux-libre source yet, then you should check if those references aren't false positives. If the first reference (eg. request_firmware_direct) is requesting a blob, then you should rename **request_firmware_direct** to **reject_firmware_direct** and if the second one (wl18xx-conf.bin) is a blob, you must replace it with ** /*(DEBLOBBED)*/ **, eg:

<code>
err = reject_firmware_direct(&ditem->fw, item->overlay_name, dev);
</code>

and

<code>
#define WL18XX_CONF_FILE_NAME "ti-connectivity/wl18xx-conf/*(DEBLOBBED)*/
</code>

<note important>If you found blobs included inside the patch, you must remove it manually with your favourite editor (eg. vim)</note>

<note important>Not all ".bin" files aren't blobs, you should check if they contains source code under a [[https://www.gnu.org/licenses/license-list.html|free license]]. Otherwise, some of them could be a short sequence of register accesses that aren't copyrightable, so the license is irrevelant and are consider false positives.</note>

<note important>deblob-check could match things such as **dtc-lexer.lex.c_shipped** as blobs, however they are false positives since are regular expression processing tables.</note>