Add Extroot Btrfs Support to Block-mount

link: http://lists.infradead.org/pipermail/lede-dev/2017-June/008117.html
link: https://openwrt.org/docs/guide-developer/feeds
link: https://wiki.openwrt.org/doc/howtobuild/single.package
link: https://wiki.openwrt.org/doc/howto/build.a.package

Change fstools makefile to newer version

link: https://git.openwrt.org/?p=project/fstools.git;a=commit
Link ahead has most updated version of fstools
Take note of commit dd02dad332958575cc52e60c78ef10ef2b5aaced
Change file Makefile

cd ~/openwrt    
git pull  
./scripts/feeds clean
./scripts/feeds update -a    
./scripts/feeds install -a 
make dirclean
wget https://downloads.lede-project.org/releases/17.01.4/targets/ar71xx/generic/config.seed 
cp config.seed .config  
make defconfig   
make package/symlinks

make menuconfig -> check M or * for block-mount 

make download  
FORCE_UNSAFE_CONFIGURE=1 make -j5 V=s tools/install
FORCE_UNSAFE_CONFIGURE=1 make -j5 V=s toolchain/install
FORCE_UNSAFE_CONFIGURE=1 make -j5 V=s target/compile

nano package/system/fstools/Makefile

#PKG_SOURCE_VERSION:=bdcb075fafdac0bfe3207c23f64acd58432bad86    
PKG_SOURCE_VERSION:=dd02dad332958575cc52e60c78ef10ef2b5aaced    

FORCE_UNSAFE_CONFIGURE=1 make -j5 V=s package/fstools/prepare 

cd build_dir/target-mips_24kc_musl-1.1.16/fstools-2017-06-30-dd02dad3/

Or Step into source file

cd build_dir/target-mips_24kc_musl-1.1.16/fstools-2017-06-30-bdcb075f/
nano block.c

./scripts/feeds install block-mount

FORCE_UNSAFE_CONFIGURE=1 make -j5 V=s package/fstools/compile
FORCE_UNSAFE_CONFIGURE=1 make -j5 V=s package/fstools/install
FORCE_UNSAFE_CONFIGURE=1 make -j5 V=s package/fstools/index

Change file block.c

--- a/block.c
+++ b/block.c
@@ -707,6 +707,7 @@ static void check_filesystem(struct probe_info *pr)
        struct stat statbuf;
        const char *e2fsck = "/usr/sbin/e2fsck";
        const char *f2fsck = "/usr/sbin/fsck.f2fs";
+       const char *btrfsck = "/usr/bin/btrfsck";
        const char *dosfsck = "/usr/sbin/dosfsck";
        const char *ckfs;

@@ -718,6 +719,8 @@ static void check_filesystem(struct probe_info *pr)
                ckfs = dosfsck;
        } else if (!strncmp(pr->type, "f2fs", 4)) {
                ckfs = f2fsck;
+       } else if (!strncmp(pr->type, "btrfs", 5)) {
+               ckfs = btrfsck;
        } else if (!strncmp(pr->type, "ext", 3)) {
                ckfs = e2fsck;
        } else {
@@ -735,6 +738,9 @@ static void check_filesystem(struct probe_info *pr)
                if(!strncmp(pr->type, "f2fs", 4)) {
                        execl(ckfs, ckfs, "-f", pr->dev, NULL);
                        exit(-1);
+               } else if(!strncmp(pr->type, "btrfs", 5)) {
+                       execl(ckfs, ckfs, "--repair", pr->dev, NULL);
+                       exit(-1);
                } else {
                        execl(ckfs, ckfs, "-p", pr->dev, NULL);
                        exit(-1);
@@ -1428,8 +1434,9 @@ static int mount_extroot(char *cfg)
        if (pr) {
                if (strncmp(pr->type, "ext", 3) &&
                    strncmp(pr->type, "f2fs", 4) &&
+                   strncmp(pr->type, "btrfs", 5) &&
                    strncmp(pr->type, "ubifs", 5)) {
-                       ULOG_ERR("extroot: unsupported filesystem %s, try ext4, f2fs or ubifs\n", pr->type);
+                       ULOG_ERR("extroot: unsupported filesystem %s, try ext4, f2fs, btrfs or ubifs\n", pr->type);
                        return -1;
                }