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Subject[PATCH] [try 3] vt: add ioctl commands to /dev/vcsaN to get/put the current palette of the given tty
From: Cedric Roux <sed@free.fr>

A ioctl interface and two ioctl commands added to /dev/vcsaN
to get/put the current palette of the given tty.

Signed-off-by: Cedric Roux <sed@free.fr>
---
This patch exists because there is no way to get the current
installed palette of a given tty. The PIO_CMAP and GIO_CMAP
in vt_ioctl.c:vt_ioctl play with the global default colormap.
And /dev/vcsaN don't dump the palette through their read
interface. And since a user may change colors of a given
tty by escape sequences, one should be able to retrieve
the palette through /dev/vcsaN, leading to this patch.

Some points I am not fully confident with:
- vt.c:set_colormap is now used in vc_screen.c so cannot be static
anymore.
The goal of this patch is to allow read access to the palette,
I can remove the PIO_CMAP case and make set_colormap static again.
This case is there because /dev/vcsaN is read/write so the access
to the palette should also be read/write. (Or I can do it
differently, no problem, just tell me how.)
- the palette is returned as it is stored in the kernel, without
taking into account color_table. So if a userland program
gets an attribute for a given character, it won't match
with the palette information. Say the user reads 0xXY through
/dev/vcsa and takes Y as an index in the palette, it will return
a bad color. One should do palette[color_table[Y]] to get the real
color.
Two "solutions" to this "problem" (it might be an non-issue):
+ export the palette by indexing with color_table:
I don't like it.
+ let the userland program deal with that:
the program may open a tty, send escape sequences to
set the current color, write a character at a given position
(through the tty, not /dev/vcs) and read back the attribute
through /dev/vcsa this time. She will see what attribute
corresponds to what color she sets by using escape sequences.
If the color_table is non-mutable, all this is a non-issue.
Userland programs just store the color_table and live with that.
I've seen no code that modifies the color_table, so I bet it's
non-mutable. (May it change in the future?)
- lock_kernel() is called. Maybe it's not necessary? I'm not
confident enough. You decide.

diff -uprN -X linux-2.6.29.1/Documentation/dontdiff linux-2.6.29.1-vanilla/drivers/char/vc_screen.c linux-2.6.29.1/drivers/char/vc_screen.c
--- linux-2.6.29.1-vanilla/drivers/char/vc_screen.c 2009-04-02 22:55:27.000000000 +0200
+++ linux-2.6.29.1/drivers/char/vc_screen.c 2009-04-14 10:16:33.000000000 +0200
@@ -19,6 +19,8 @@
* machek@k332.feld.cvut.cz - modified not to send characters to wrong console
* - fixed some fatal off-by-one bugs (0-- no longer == -1 -> looping and looping and looping...)
* - making it shorter - scr_readw are macros which expand in PRETTY long code
+ *
+ * Colormap put/get for /dev/vcsaN, Cedric Roux <sed@free.fr>, March 2009.
*/

#include <linux/kernel.h>
@@ -470,11 +472,67 @@ vcs_open(struct inode *inode, struct fil
return ret;
}

+static long
+vcs_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+ unsigned int currcons = iminor(file->f_path.dentry->d_inode);
+ struct vc_data *vc;
+ unsigned char pal[16*3];
+ long ret = 0;
+
+ /* access only defined for /dev/vcsaN, not /dev/vcsN */
+ if (currcons < 128)
+ return -ENOTTY;
+
+ lock_kernel();
+
+ acquire_console_sem();
+
+ currcons &= 127;
+ if (currcons == 0)
+ currcons = fg_console;
+ else
+ currcons--;
+ if (!vc_cons_allocated(currcons)) {
+ ret = -ENXIO;
+ goto unlock_out;
+ }
+ vc = vc_cons[currcons].d;
+
+ switch (cmd) {
+ case PIO_CMAP:
+ if (copy_from_user(pal, (void __user *)arg, 16*3)) {
+ ret = -EFAULT;
+ goto unlock_out;
+ }
+ memcpy(vc->vc_palette, pal, 16*3);
+ set_palette(vc);
+ break;
+ case GIO_CMAP:
+ if (copy_to_user((void __user *)arg, vc->vc_palette, 16*3)) {
+ ret = -EFAULT;
+ goto unlock_out;
+ }
+ break;
+ default:
+ ret = -ENOIOCTLCMD;
+ break;
+ }
+
+unlock_out:
+ release_console_sem();
+
+ unlock_kernel();
+
+ return ret;
+}
+
static const struct file_operations vcs_fops = {
.llseek = vcs_lseek,
.read = vcs_read,
.write = vcs_write,
.open = vcs_open,
+ .unlocked_ioctl = vcs_ioctl,
};

static struct class *vc_class;
diff -uprN -X linux-2.6.29.1/Documentation/dontdiff linux-2.6.29.1-vanilla/drivers/char/vt.c linux-2.6.29.1/drivers/char/vt.c
--- linux-2.6.29.1-vanilla/drivers/char/vt.c 2009-04-02 22:55:27.000000000 +0200
+++ linux-2.6.29.1/drivers/char/vt.c 2009-04-14 10:17:20.000000000 +0200
@@ -156,7 +156,6 @@ static void set_cursor(struct vc_data *v
static void hide_cursor(struct vc_data *vc);
static void console_callback(struct work_struct *ignored);
static void blank_screen_t(unsigned long dummy);
-static void set_palette(struct vc_data *vc);

static int printable; /* Is console ready for printing? */
int default_utf8 = true;
@@ -3753,7 +3752,7 @@ void poke_blanked_console(void)
* Palettes
*/

-static void set_palette(struct vc_data *vc)
+void set_palette(struct vc_data *vc)
{
WARN_CONSOLE_UNLOCKED();

diff -uprN -X linux-2.6.29.1/Documentation/dontdiff linux-2.6.29.1-vanilla/include/linux/vt_kern.h linux-2.6.29.1/include/linux/vt_kern.h
--- linux-2.6.29.1-vanilla/include/linux/vt_kern.h 2009-04-02 22:55:27.000000000 +0200
+++ linux-2.6.29.1/include/linux/vt_kern.h 2009-04-14 10:17:59.000000000 +0200
@@ -97,6 +97,7 @@ void reset_vc(struct vc_data *vc);
extern int unbind_con_driver(const struct consw *csw, int first, int last,
int deflt);
int vty_init(const struct file_operations *console_fops);
+void set_palette(struct vc_data *vc);

/*
* vc_screen.c shares this temporary buffer with the console write code so that

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