[OpenWrt-Devel] [PATCH V3] Re: procd: patch to support busybox mkfs.ext2

Luke McKee hojuruku at gmail.com
Sun Jul 3 05:29:54 EDT 2016

On 07/03/2016 01:24 PM, John Crispin wrote:
> Hi,
> few comments
> 1) the patch needs to be split into 2, ext2 change/lzo change
> 2) send them inline please and not as attachement
> 3) the V3 needs to be in the subject prefix [PATCH V3] procd: ...
> 4) the Signed-off-by: line is missing
> 	John

Hi John,

1) no can do. You are going to merge it into your project git page
anyway, unless openwrt locked you out of your own project you are a
maintainer of on git. In which case reply with the rebuke to .... 2) ok
I fired up thunderbird, google mail destroys patches in plain text mode
3) done 4) done

Don't blame me for the long email. I thought I was already done earlier
but .....

I have tested this with lede trunk with v2 of the patch. V3 is the same
just with a #ifdef, lz4 (faster less compression). It definitely works.
It has 4mb flash.

140k of text files generated in my setup and placed in /tmp turned into
7.1k - neat! - however tmpfs has garbage collection zram doesn't exit
unless you create a cron job that will dd if=/dev/zero bs=4096
of=/tmp/zero.bin count=sizeofreespace; rm /tmp/zero.bin. Deleting a file
from /tmp doesn't allow memory reclamation like with tmpfs. Under normal
use it will take a long time for this to really fill up, especially if
ext2 is over-writing the same files & inodes. Zram module estimates
there is 28meg of /tmp storage which is more than you'd get with tmpfs.
My tp-link has 32mb ram 28 usable.

Secure deletion on ext4 was never popular: https://lwn.net/Articles/462437/

Also of NOTE is tmpfs is STILL getting mounted. People with this feature
on could in theory disable tmpfs. John you might want to look into
disabling the tmpfs mount of ZRAM_TMPFS mounted instead.


Constraints for the Makefile for procd to go with this I didn't submit,
because I'm not sure config stanzas like package stanzas can have
DEPENDS. Maybe you have to make it a fake package or something that
really just passes on the defines to gcc so you can set up package


1) Thou shall turn on CONFIG_BUSYBOX_CONFIG_MKFS_EXT2=y

Justification: ~15-20k binary vs 350k (with stripping) for mkfs.ext2 and
if you want the proper mkfs.ext4 etc you can install it in your overlay
- extroot. Busybox mkfs.ext2 and e2fsprogs are configured not to collide
with each-other.  This patch makes the need for e2fsprogs libext2
redundant. Not having this (like we do right now) will flood the bug
reports with idiots (like me) wondering why they bricked their router
when it can't mount /tmp.

2) Debatable: Thou shall disable zram-swap, zram-swap shall block this

Justification: Right now they both want to use /dev/zram0, but the
system will have no space for running apps if they are both running at
the same time. You need to allocate 1/3 ram to each at best. That will
have be a new compile time option in a further patch, that I will
release should someone make the argument for wanting both of these.

You either want 1 of 3 possible setups. #1 This patch. Best for people
who need to opkg -d ram a lot of stuff #2 tmpfs and progs BOTH can use
zram-swap which makes it a better overall choice, after thinking about
this patch it isn't worth it as much as just using zram-swap. But better
have a working feature than a broken one as it exists in buildroot now
Or #3 Assuming you have a fast storage device connected to your openwrt
(most don't but some NASes do) ZSWAP kernel will dynamically use free
memory to offer a pre-swap cache, and allow compressed data (lzo/lz4) to
be wrote to swap. It may require an actual initialized swap device to
work. I haven't RTFMed yet.

3) Debatable: LZ4 should be on by default. (My two cents)

Justification: It's almost compresses well as LZO but it's less CPU
intensive for those without Floating point SMID's which is most home
routers. So put some help about that in the Makefile. LZ4 is included as
a dependency to the zram.ko module and will be loaded at early boot by
modprobe / procd. Contrary to  rumors circulating on openwrt's trac it
actually works :) https://dev.openwrt.org/ticket/22666#comment:3

4) Highly recommended: Makefile should block option if your kernel isn't

Justification: https://dev.openwrt.org/ticket/21705 & above

5) Stop openwrt folks trying to patch the kernel to make two zram
devices by default because you can hot-add them.


Here's the patch


procd: remove dependency on bloated e2fsprogs/libext2 and use

At a minimum (see accompanying email on mailing list) advising my two
cents on the pros and cons of this patch
you need to add a configuration option to the Makefile if you want lz4

    default n
    prompt "Mount /tmp using zram."


Signed-off-by: Luke McKee <hojuruku at gmail.com>

--- a/initd/zram.c    2016-07-03 06:39:51.011999930 +0700
+++ b/initd/zram.c    2016-07-03 07:00:34.143492847 +0700
@@ -82,7 +82,7 @@
-    char *mkfs[] = { "/usr/sbin/mkfs.ext4", "-b", "4096", "-F", "-L",
"TEMP", "-m", "0", "/dev/zram0", NULL };
+    char *mkfs[] = { "/sbin/mkfs.ext2", "-b", "4096", "-F", "-L",
"TEMP", "-m", "0", "/dev/zram0", NULL };
     FILE *fp;
     long zramsize;
     pid_t pid;
@@ -94,6 +95,15 @@
     mkdev("*", 0600);
+#ifdef ZRAM_TMPFS_LZ4   
+    fp = fopen("/sys/block/zram0/comp_algorithm", "r+");
+    if (fp == NULL) {
+        ERROR("Can't open /sys/block/zram0/comp_algorithm: %s\n",
+        return errno;
+    }
+    fprintf(fp, "%s", "lz4" );
+    fclose(fp);
     zramsize = proc_meminfo() / 2;
     fp = fopen("/sys/block/zram0/disksize", "r+");
@@ -107,10 +116,10 @@
     pid = fork();
     if (!pid) {
         execvp(mkfs[0], mkfs);
-        ERROR("Can't exec /sbin/mkfs.ext4\n");
+        ERROR("Can't exec /sbin/mkfs.ext2\n");
     } else if (pid <= 0) {
-        ERROR("Can't exec /sbin/mkfs.ext4\n");
+        ERROR("Can't exec /sbin/mkfs.ext2\n");
         return -1;
     } else {
         waitpid(pid, NULL, 0);
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