On Wed, Sep 30, 2020 at 12:56 PM Peilin Ye yepeilin.cs@gmail.com wrote:
On Wed, Sep 30, 2020 at 11:53:17AM +0200, Daniel Vetter wrote:
On Wed, Sep 30, 2020 at 03:11:51AM -0400, Peilin Ye wrote:
On Tue, Sep 29, 2020 at 04:38:49PM +0200, Daniel Vetter wrote:
On Tue, Sep 29, 2020 at 2:34 PM Peilin Ye yepeilin.cs@gmail.com wrote:
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
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! :)
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...
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