On Wed, Sep 30, 2020 at 12:56 PM Peilin Ye [off-list ref] wrote:

On Wed, Sep 30, 2020 at 11:53:17AM +0200, Daniel Vetter wrote:

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On Wed, Sep 30, 2020 at 03:11:51AM -0400, Peilin Ye wrote:

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On Tue, Sep 29, 2020 at 04:38:49PM +0200, Daniel Vetter wrote:

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On Tue, Sep 29, 2020 at 2:34 PM Peilin Ye [off-list ref] wrote:

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Ah, and speaking of built-in fonts, see fbcon_startup():

        /* Setup default font */
                [...]
                vc->vc_font.charcount = 256; /* FIXME  Need to support more fonts */
                            ^^^^^^^^^^^^^^^

This is because find_font() and get_default_font() return a `struct
font_desc *`, but `struct font_desc` doesn't contain `charcount`. I
think we also need to add a `charcount` field to `struct font_desc`.

Hm yeah ... I guess maybe struct font_desc should be the starting
point for the kernel internal font structure. It's at least there
already ...

I see, that will also make handling built-in fonts much easier!

I think the only downside with starting with font_desc as the internal
font represenation is that there's a few fields we don't need/have for
userspace fonts (like the id/name stuff). So any helpers to e.g. print out
font information need to make sure they don't trip over that

But otherwise I don't see a problem with this, I think.

Yes, and built-in fonts don't use refcount. Or maybe we can let
find_font() and get_default_font() kmalloc() a copy of built-in font
data, then keep track of refcount for both user and built-in fonts, but
that will waste a few K of memory for each built-in font we use...

A possible trick for this would be to make sure built-in fonts start
out with a refcount of 1. So never get freed. Plus maybe a check that
if the name is set, then it's a built-in font and if we ever underflow
the refcount we just WARN, but don't free anything.

Another trick would be kern_font_get/put wrappers (we'd want those
anyway if the userspace fonts are refcounted) and if kern_font->name
!= NULL (i.e. built-in font with name) then we simply don't call
kref_get/put.
-Daniel

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I think for vc_date->vc_font we might need a multi-step approach:
- first add a new helper function which sets the font for a vc using
an uapi console_font struct (and probably hard-coded assumes cnt =
256.

But user fonts may have a charcount different to 256... But yes I'll try
to figure out how.

Hm yeah, maybe we need a helper to give us the charcount then, which by
default is using the magic negative offset.

Ah, I see! :)

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Then once we've converted everything over to explicitly passing charcount
around, we can switch that helper. So something like

int kern_font_charcount(struct kern_font *font);

Feel free to bikeshed the struct name however you see fit :-)

I think both `kern_font` and `font_desc` makes sense, naming is so
hard...

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For first steps I'd start with demidlayering some of the internal
users of uapi structs, like the console_font_op really shouldn't be
used anywhere in any function, except in the ioctl handler that
converts it into the right function call. You'll probably discover a
few other places like this on the go.

Sure, I'll start from this, then cleaning up these dummy functions, then
`vc_data`. Thank you for the insights!

Please don't take this rough plan as fixed, it's just where I'd start from
browsing the code and your analysis a bit. We'll probably have to adapt as
we go and more nasty things turn up ...

Sure, I'll first give it a try and see. Thank you!

Peilin Ye

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch