[U-Boot] [PATCH] tools/fw_env: use fsync to ensure that data is physically stored

[Mark Jackson <mpfj-list@newflow.co.uk>]

On 21/05/13 18:34, Michael Heimpold wrote:
> Hi Wolfgang Denx,
> 
>>> Closing a file descriptor does not guarantee that the data has been
>>> successfully saved to disk, as the kernel might defer the write.
>>
>> What is the exact problem you are trying to fix?
>>
>> I mean, when exactly does adding the sync play a role?
> 
> I'm using fw_setenv during system update process. The sequence
> of such a shell script is something like (much simplified):
> 
> ...
> fw_setenv state=2
> dd if=... of=/dev/mmcblk0...
> fw_setenv state=1
> ...
> reboot

Not sure what final "OS" environment you're running, but I would think
that "reboot" would sync for you ?

For instance, under BusyBox, we have:-

# reboot --help
BusyBox v1.14.0 (2012-02-15 10:28:26 GMT) multi-call binary

Usage: reboot [-d delay] [-n] [-f]

Reboot the system

Options:
	-d	Delay interval for rebooting
	-n	No call to sync()
	-f	Force reboot (don't go through init)

... and under Ubuntu, we have ...

$ reboot --help
Usage: reboot [OPTION]...
Reboot the system.

Options:
  -n, --no-sync               don't sync before reboot or halt
...

So by default, reboot would (should ?) call sync automatically.

This might point to some other issue ?

Mark J.