rtems-examples hello no output devfs

[Sebastian Huber]

On 14/02/2020 15:45, Joel Sherrill wrote:

> On Fri, Feb 14, 2020 at 7:08 AM Sebastian Huber 
> <sebastian.huber at embedded-brains.de 
> <mailto:sebastian.huber at embedded-brains.de>> wrote:
>
>     On 14/02/2020 13:57, Joel Sherrill wrote:
>
>     > Hi
>     >
>     > I haven't investigated or checked on other bsps but the xilinx qemu
>     > bsp has no output with the hello world in examples. It uses the
>     devfs.
>     > Changing it to the default filesystem results in it working.
>     >
>     > I am suspicious of something with all the termios and new console
>     > changes breaking it.
>     The devfs works only with legacy IO drivers. The Termios drivers
>     depend
>     on IMFS. I would like to remove the devfs in the future. The IMFS is
>     highly configurable, there is no need for an additional in-memory
>     file
>     system.
>
>
> Do not remove it. Please fix it.

The IMFS should be improved, so that we can remove the devfs. We already 
have a bunch of configuration options to customize it:

https://docs.rtems.org/branches/master/c-user/configuring_a_system.html#file-system-configuration-parameters

>
> This filesystem is needed because some applications want no filesystem but
> you require one for device nodes. Even the IMFS is subject to mallocs 
> which
> are undesired in the applications that this was supporting.

Termios uses malloc(), so I don't think this filesystem makes sense for 
console drivers. I changed the clock driver to use a simple system 
initialization handler. Some time ago I refactored the IMFS mount 
operation to use statically allocated data:

https://git.rtems.org/rtems/commit/?id=a9df9169882c564af6714bbf121c278092d3c51c

With a bit of work the IMFS_make_generic_node() can be changed to not 
allocate memory and instead use memory provided by the caller. I spend a 
considerable amount of time to make it possible that some time in the 
future we can have applications with purely statically allocated resources.

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