Re: [Minios-devel] [UNIKRAFT PATCH v2 0/6] Move VFS initialization to ukboot

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

On 08.09.19 17:05, Costin Lupu wrote:
> Hi Simon,
>
> We clearly need to come up with a solution for initializing filesystems.
> However, these series have to be reworked:
> 1. You should add your changes once > 2. We should add this init thing in 
> vfscore instead of bloating the
> boot.c code.
I originally chose libukboot because of our current boot logic. The 
reason is that we should not use any pre-init or init table entries for 
our system initialization. We should treat the tables as reserved to the 
Unikernel(-ized) program and its libraries. So far we used them for the 
case when we need memory and/or scheduling support. However, whenever we 
port existing standard user space programs (e.g., Linux program) to our 
environment, we actually should be aware that its constructor and init 
functions interact already with or system components. Effectively, they 
should be fully initialized at that point. I expect that most 
interactions are done with the VFS.
Overall our current boot stages should look like this:

 0) Entry and early platform init (platform library)
 1) Unikraft constructors
    Cannot use ukalloc or uksched because it is not initialized yet.
 2) Unikraft init
    2.1) ukalloc
    2.2) uksched
    2.3) VFS
    2.4) Networking
    2.5) etc.
 3) Program constructors
    These are the entries that we find in the pre-init and init
    sections.
 4) Enter main() of the program

Everything of point 2 is currently hard-coded to libukboot. So it makes 
currently sense to put our VFS initialization there instead of 
registering it to the pre-init or init section. In fact, I agree that we 
need to introduce a "Unikraft init table" (similar to Unikraft 
constructors) where our system libraries can register themselves to. As 
intermediate solution I could introduce a vfscore_init() function that 
is called from libukboot, similar to what we did with lwip. This way, we 
keep the VFS init code in vfscore.
However, I also had a second reason for putting the VFS init code to 
libukboot: I had in mind that we could add initrd support with another 
patch series relatively easy:
 1) Mount ramfs for /
 2) Search for an archive in initrd section
 3) Decompress archive to /
 4) Add initrd memory region to initialized ukalloc
    because we do not need it anymore.

A decompressing algorithm that creates directories and files from the 
archive (e.g., based on zlib) is the only missing piece. No. 4 requires 
knowledge about which allocator to add memory regions to. This would be 
currently much easier with libukboot that could dictate this. However, 
we can also find another solution for doing this when implementing 
initrd support as part of vfscore...
What do you think?

> Cheers,
> Costin
>
> On 9/6/19 3:03 PM, Simon Kuenzer wrote:
> > This patch series moves mounting filesystems as part of the Unikraft
> > initialization to lib/ukboot. This will later simplify adding more features
> > to the automount code because it is at a single place (e.g., loading initrd
> > as root filesystem, enable mounting 9pfs shares as root mountpoint).
> >
> > Previously, the option to automatically mount a ramfs to / was hidden.
> > It only appeared when devfs was selected. This series is also making devfs
> > and ramfs permanently visible in the menu to simplify the usage.
> >
> > Changes since v1:
> >   - Adopt to latest staging state
> >   - Add ability to configure root fs with kernel parameters
> >
> > Simon Kuenzer (6):
> >    lib/ukboot: Application constructors right before calling application
> >    lib/devfs, lib/ukboot: Move option to automatically mount root to
> >      libukboot
> >    lib/ukboot: devfs automount option
> >    lib/ramfs: Config.uk: Use select for dependency
> >    lib/ukswrand: Clean-up: devfs nodes are independent of MWC algorithm
> >    lib/ukboot: Root filesystem as library parameter
> >
> >   lib/devfs/Config.uk               |   8 +--
> >   lib/devfs/devfs_vnops.c           |  25 --------
> >   lib/ramfs/Config.uk               |   2 +-
> >   lib/ukboot/Config.uk              |  29 +++++++++
> >   lib/ukboot/Makefile.uk            |   3 +
> >   lib/ukboot/boot.c                 | 102 +++++++++++++++++++++++-------
> >   lib/ukswrand/Config.uk            |   5 +-
> >   lib/ukswrand/Makefile.uk          |   6 +-
> >   lib/ukswrand/{mwc_dev.c => dev.c} |  26 +++++---
> >   9 files changed, 134 insertions(+), 72 deletions(-)
> >   rename lib/ukswrand/{mwc_dev.c => dev.c} (83%)
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