Re: [Linux-fbdev-devel] Re: [PATCH] fbdev: colormap fixes
From: Jon Smirl
Date: Thu Jul 28 2005 - 11:36:35 EST
On 7/28/05, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> On Thu, 28 Jul 2005, Antonino A. Daplas wrote:
> > Jon Smirl wrote:
> > > On 7/28/05, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> > > > On Wed, 27 Jul 2005, Linux Kernel Mailing List wrote:
> > >
> > > There are a couple of ways to fix this.
> > > 1) Add a check to limit use of the sysfs attributes to 256 entries. If
> > > you want more you have to use /dev/fb0 and the ioctl. More is an
> > > uncommon case.
> > > 2) Switch this to a binary parameter. Now you have to use tools like
> > > hexdump instead of cat to work with the data. It was nice to be able
> > > to use cat to see the current map.
> > >
> > > Does anyone have preferences for which way to fix it?
> > Or...
> > 3) Add another file in sysfs which specifies at what index and how many
> > entries will be read or written from or to the cmap. With this additional
> > sysfs file, it should be able to handle any reasonable cmap length, but
> > it will take more than one reading of the color_map file. Another
> > advantage is that the entire color map need not be read or written if
> > only one field needs to be changed.
> > I've attached a test patch. Let me know what you think.
> I like it! ... But, a disadvantages is that it needs to store state between two
> non-atomic operations. E.g. imagine two processes doing this at the same time.
Two attributes is a big problem with atomicity. If you want access to
the full cmap I would switch to a binary attribute or use the existing
Note that you can set the entire map with the new patch, you just
can't read it. You can store 1-N entries at any base you want.
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
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