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6b8407c6da
OpenWrt uses a lot of (b)ash scripts for initial setup. This isn't the
best solution as they almost never consider syncing files / data. Still
this is what we have and we need to try living with it.
Without proper syncing OpenWrt can easily get into an inconsistent state
on power cut. It's because:
1. Actual (flash) inode and data writes are not synchronized
2. Data writeback can take up to 30 seconds (dirty_expire_centisecs)
3. ubifs adds extra 5 seconds (dirty_writeback_centisecs) "delay"
Some possible cases (examples) for new files:
1. Power cut during 5 seconds after write() can result in all data loss
2. Power cut happening between 5 and 35 seconds after write() can result
in empty file (inode flushed after 5 seconds, data flush queued)
Above affects e.g. uci-defaults. After executing some migration script
it may get deleted (whited out) without generated data getting actually
written. Power cut will result in missing data and deleted file.
There are three ways of dealing with that:
1. Rewriting all user-space init to proper C with syncs
2. Trying bash hacks (like creating tmp files & moving them)
3. Adding sync and hoping for no power cut during critical section
This change introduces the last solution that is the simplest. It
reduces time during which things may go wrong from ~35 seconds to
probably less than a second. Of course it applies only to IO operations
performed before /etc/init.d/boot . It's probably the stage when the
most new files get created.
All later changes are usually done using smarter C apps (e.g. busybox or
uci) that creates tmp files and uses rename() that is expected to be
atomic.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
(cherry picked from commit
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| .github | ||
| config | ||
| include | ||
| package | ||
| scripts | ||
| target | ||
| toolchain | ||
| tools | ||
| .gitattributes | ||
| .gitignore | ||
| BSDmakefile | ||
| Config.in | ||
| feeds.conf.default | ||
| LICENSE | ||
| Makefile | ||
| README | ||
| rules.mk | ||
_______ ________ __
| |.-----.-----.-----.| | | |.----.| |_
| - || _ | -__| || | | || _|| _|
|_______|| __|_____|__|__||________||__| |____|
|__| W I R E L E S S F R E E D O M
-----------------------------------------------------
This is the buildsystem for the OpenWrt Linux distribution.
To build your own firmware you need a Linux, BSD or MacOSX system (case
sensitive filesystem required). Cygwin is unsupported because of the lack
of a case sensitive file system.
You need gcc, binutils, bzip2, flex, python, perl, make, find, grep, diff,
unzip, gawk, getopt, subversion, libz-dev and libc headers installed.
1. Run "./scripts/feeds update -a" to obtain all the latest package definitions
defined in feeds.conf / feeds.conf.default
2. Run "./scripts/feeds install -a" to install symlinks for all obtained
packages into package/feeds/
3. Run "make menuconfig" to select your preferred configuration for the
toolchain, target system & firmware packages.
4. Run "make" to build your firmware. This will download all sources, build
the cross-compile toolchain and then cross-compile the Linux kernel & all
chosen applications for your target system.
Sunshine!
Your OpenWrt Community
http://www.openwrt.org