[LEDE-DEV] "block" fstools wishlist

[John Crispin]

On 20/05/2016 02:24, Daniel Golle wrote:
> Hi Karl,
> 
> I thought a bit about fstools since your post because I also had my
> difficulties integrating it with applications which require hotplug
> storage. I agree with and acknowledge all the points you mentioned.
> 
> In addition I believe that LEDE/OpenWrt generally lacks a high-level
> concept to integrate optional block storage. Imho something like /data
> on Android (or just mount it to /var?) would be nice and make setting
> up services much easier, also without using extroot. Just a missing
> convention to agree on.
> It could be a symlink to /mnt/sda1 or /mnt/mmcblock0p1 or whatever
> is detected first on a specific device. autofs4 with mountd does the
> job well imho, I didn't have problems with that.
> What's needed are sane defaults depending on the type of hardware
> (both, board-type and detected storage peripherals). And a simple
> one-click "initialize storage device XYZ and use it per default for all
> on this system". That should do partitioning, mkfs and setup fstab.
> More complex setups with md raid or even LVM2 and cryptsetup mark the
> top-edge of the model.
> 
> I suggest we should draft the structures and api in some etherpad and
> then implement an *optional* storage management service based on
> fstools and replacing/extending block-mount. Adding hotplug handlers
> for block devices should then become rather trivial.
> 
> It'd also be nice to have a "large block storage is now mounted"
> runlevel, so services depending on that (think: squid, postgresql,
> git server, ...) would be started only once the block device has
> settled and was mounted.
> 
> This would allow things like databases or other apps which require
> storage to create their filessytem structures automatically in the
> package's post-inst-on-target aka. uci-defaults script and have a sane
> default set in their configurations.
> (I'd very much like to have that e.g. for postgresql, and also offer
> some functions in a to-be-created /lib/functions/postgresql.sh for
> packages to setup databases)
> 
> If anyone can setup an etherpad in the meantime I'll happily start
> adding my suggestings to the spec once I got some sleep...
> 
> 
> Cheers
> 
> 
> Daniel
> 

added a few things here, please add what you think should also be added

http://piratepad.net/2le3wZujiS

	John



> 
> 
> 
> On Wed, May 18, 2016 at 04:45:57PM -0000, Karl Palsson wrote:
>>
>> Listing out a few things I've found with fstools package
>> (Version: 2016-05-17-db5d39d48b9d9a77565015c1aafb3ef0d2925f02)
>> I'm mostly still working on openwrt CC branch, but the issues
>> _seem_ to be fstools related, not kernel related, though I'm
>> happy to retest if necessary. Some of these I've discussed on irc
>> with blogic and jow, others just here, posting them here for
>> posterity as they're bigger than quick fixes on IRC. Further,
>> this is largely an area I'm not really comfortable trying to hack
>> up patches, they need to follow the style and direction of the
>> project more than just my specific needs, so I can't post patches
>> for any of these.
>>
>> * block mount mounts _and_ turns swap on.  block umount only unmounts.  Shouldn't it swapoff as well?
>>
>> * "block" anything can't have it's output captured.  The checks in libubox: ulog.c:: ulog_defaults() detect the attempt at capturing the output as a !tty and write to syslog instead.  
>>
>> * block doesn't handle hotplug.  This is probably the biggest thing. This overlaps with the old and unmaintained "mountd" package, which blogic expressed interesting destroying/merging/combining with "fstools"  This doesn't seem to be a problem for usb sticks, because the removal of the stick removes the entire device node well.  However, an SD card in a slot maintains a /dev/sda entry even after the card is removed.  "block info" will fail to see new block details if a partition was mounted, or as activated swap, and swap and mounts are not turned off when the card is removed.
>>
>> I wrote about various trials and tribulations with mountd vs
>> block here
>> https://lists.openwrt.org/pipermail/openwrt-devel/2016-February/039798.html
>> and resolved that I would simply poll "block info" every couple
>> of seconds. Unfortunately, that ended up being rather noticeable
>> CPU load, so I'm still looking for neat ways of handling sdcards,
>> and while mountd noticed disk changes, it failed at reliably
>> mounting/unmounting, and most importantly, was and is clearly
>> regarded as "not the right way" going forward.
>>
>> Desktop linux mostly solves this with udisks/udisks2, and at the moment, something functionally equivalent is rather missing from the lede user space world.  
>>
>> Cheers,
>> Karl P
> 
> 
> 
> 
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