vt: introduce unicode mode for /dev/vcs

Now that the core vt code knows how to preserve unicode values for each
displayed character, it is then possible to let user space access it via
/dev/vcs*.

Unicode characters are presented as 32 bit values in native endianity
via the /dev/vcsu* devices, mimicking the simple /dev/vcs* devices.
Unicode with attributes (similarly to /dev/vcsa*) is not supported at
the moment.

Data is available only as long as the console is in UTF-8 mode. ENODATA
is returned otherwise.

This was tested with the latest development version (to become
version 5.7) of BRLTTY. Amongst other things, this allows ⠋⠕⠗ ⠞⠓⠊⠎
⠃⠗⠁⠊⠇⠇⠑⠀⠞⠑⠭⠞⠀to appear directly on braille displays regardless of the
console font being used.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Tested-by: Dave Mielke <Dave@mielke.cc>
Acked-by: Adam Borowski <kilobyte@angband.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 141 insertions, 14 deletions

diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index e4a66e1fd05f..9c44252e52a3 100644
--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -10,6 +10,12 @@
  *      Attribute/character pair is in native endianity.
  *            [minor: N+128]
  *
+ * /dev/vcsuN: similar to /dev/vcsaN but using 4-byte unicode values
+ *      instead of 1-byte screen glyph values.
+ *            [minor: N+64]
+ *
+ * /dev/vcsuaN: same idea as /dev/vcsaN for unicode (not yet implemented).
+ *
  * This replaces screendump and part of selection, so that the system
  * administrator can control access using file system permissions.
  *
@@ -51,6 +57,26 @@
 
 #define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 256 : PAGE_SIZE)
 
+/*
+ * Our minor space:
+ *
+ *   0 ... 63   glyph mode without attributes
+ *  64 ... 127  unicode mode without attributes
+ * 128 ... 191  glyph mode with attributes
+ * 192 ... 255  unused (reserved for unicode with attributes)
+ *
+ * This relies on MAX_NR_CONSOLES being  <= 63, meaning 63 actual consoles
+ * with minors 0, 64, 128 and 192 being proxies for the foreground console.
+ */
+#if MAX_NR_CONSOLES > 63
+#warning "/dev/vcs* devices may not accommodate more than 63 consoles"
+#endif
+
+#define console(inode)          (iminor(inode) & 63)
+#define use_unicode(inode)      (iminor(inode) & 64)
+#define use_attributes(inode)   (iminor(inode) & 128)
+
+
 struct vcs_poll_data {
         struct notifier_block notifier;
         unsigned int cons_num;
@@ -102,7 +128,7 @@ vcs_poll_data_get(struct file *file)
         poll = kzalloc(sizeof(*poll), GFP_KERNEL);
         if (!poll)
                 return NULL;
-        poll->cons_num = iminor(file_inode(file)) & 127;
+        poll->cons_num = console(file_inode(file));
         init_waitqueue_head(&poll->waitq);
         poll->notifier.notifier_call = vcs_notifier;
         if (register_vt_notifier(&poll->notifier) != 0) {
@@ -140,7 +166,7 @@ vcs_poll_data_get(struct file *file)
 static struct vc_data*
 vcs_vc(struct inode *inode, int *viewed)
 {
-        unsigned int currcons = iminor(inode) & 127;
+        unsigned int currcons = console(inode);
 
         WARN_CONSOLE_UNLOCKED();
 
@@ -164,7 +190,6 @@ static int
 vcs_size(struct inode *inode)
 {
         int size;
-        int minor = iminor(inode);
         struct vc_data *vc;
 
         WARN_CONSOLE_UNLOCKED();
@@ -175,8 +200,12 @@ vcs_size(struct inode *inode)
 
         size = vc->vc_rows * vc->vc_cols;
 
-        if (minor & 128)
+        if (use_attributes(inode)) {
+                if (use_unicode(inode))
+                        return -EOPNOTSUPP;
                 size = 2*size + HEADER_SIZE;
+        } else if (use_unicode(inode))
+                size *= 4;
         return size;
 }
 
@@ -197,12 +226,10 @@ static ssize_t
 vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 {
         struct inode *inode = file_inode(file);
-        unsigned int currcons = iminor(inode);
         struct vc_data *vc;
         struct vcs_poll_data *poll;
-        long pos;
-        long attr, read;
-        int col, maxcol, viewed;
+        long pos, read;
+        int attr, uni_mode, row, col, maxcol, viewed;
         unsigned short *org = NULL;
         ssize_t ret;
         char *con_buf;
@@ -218,7 +245,8 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
          */
         console_lock();
 
-        attr = (currcons & 128);
+        uni_mode = use_unicode(inode);
+        attr = use_attributes(inode);
         ret = -ENXIO;
         vc = vcs_vc(inode, &viewed);
         if (!vc)
@@ -227,6 +255,10 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
         ret = -EINVAL;
         if (pos < 0)
                 goto unlock_out;
+        /* we enforce 32-bit alignment for pos and count in unicode mode */
+        if (uni_mode && (pos | count) & 3)
+                goto unlock_out;
+
         poll = file->private_data;
         if (count && poll)
                 poll->seen_last_update = true;
@@ -266,7 +298,27 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
                 con_buf_start = con_buf0 = con_buf;
                 orig_count = this_round;
                 maxcol = vc->vc_cols;
-                if (!attr) {
+                if (uni_mode) {
+                        unsigned int nr;
+
+                        ret = vc_uniscr_check(vc);
+                        if (ret)
+                                break;
+                        p /= 4;
+                        row = p / vc->vc_cols;
+                        col = p % maxcol;
+                        nr = maxcol - col;
+                        do {
+                                if (nr > this_round/4)
+                                        nr = this_round/4;
+                                vc_uniscr_copy_line(vc, con_buf0, row, col, nr);
+                                con_buf0 += nr * 4;
+                                this_round -= nr * 4;
+                                row++;
+                                col = 0;
+                                nr = maxcol;
+                        } while (this_round);
+                } else if (!attr) {
                         org = screen_pos(vc, p, viewed);
                         col = p % maxcol;
                         p += maxcol - col;
@@ -375,7 +427,6 @@ static ssize_t
 vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 {
         struct inode *inode = file_inode(file);
-        unsigned int currcons = iminor(inode);
         struct vc_data *vc;
         long pos;
         long attr, size, written;
@@ -396,7 +447,7 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
          */
         console_lock();
 
-        attr = (currcons & 128);
+        attr = use_attributes(inode);
         ret = -ENXIO;
         vc = vcs_vc(inode, &viewed);
         if (!vc)
@@ -593,9 +644,15 @@ vcs_fasync(int fd, struct file *file, int on)
 static int
 vcs_open(struct inode *inode, struct file *filp)
 {
-        unsigned int currcons = iminor(inode) & 127;
+        unsigned int currcons = console(inode);
+        bool attr = use_attributes(inode);
+        bool uni_mode = use_unicode(inode);
         int ret = 0;
-        
+
+        /* we currently don't support attributes in unicode mode */
+        if (attr && uni_mode)
+                return -EOPNOTSUPP;
+
         console_lock();
         if(currcons && !vc_cons_allocated(currcons-1))
                 ret = -ENXIO;
@@ -628,6 +685,8 @@ void vcs_make_sysfs(int index)
 {
         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL,
                       "vcs%u", index + 1);
+        device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 65), NULL,
+                      "vcsu%u", index + 1);
         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL,
                       "vcsa%u", index + 1);
 }
@@ -635,6 +694,7 @@ void vcs_make_sysfs(int index)
 void vcs_remove_sysfs(int index)
 {
         device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 1));
+        device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 65));
         device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 129));
 }
 
@@ -647,6 +707,7 @@ int __init vcs_init(void)
         vc_class = class_create(THIS_MODULE, "vc");
 
         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 0), NULL, "vcs");
+        device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 64), NULL, "vcsu");
         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 128), NULL, "vcsa");
         for (i = 0; i < MIN_NR_CONSOLES; i++)
                 vcs_make_sysfs(i);
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 7b636638b36d..062ce6be7957 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -481,6 +481,67 @@ static void vc_uniscr_copy_area(struct uni_screen *dst,
         }
 }
 
+/*
+ * Called from vcs_read() to make sure unicode screen retrieval is possible.
+ * This will initialize the unicode screen buffer if not already done.
+ * This returns 0 if OK, or a negative error code otherwise.
+ * In particular, -ENODATA is returned if the console is not in UTF-8 mode.
+ */
+int vc_uniscr_check(struct vc_data *vc)
+{
+        struct uni_screen *uniscr;
+        unsigned short *p;
+        int x, y, mask;
+
+        if (__is_defined(NO_VC_UNI_SCREEN))
+                return -EOPNOTSUPP;
+
+        WARN_CONSOLE_UNLOCKED();
+
+        if (!vc->vc_utf)
+                return -ENODATA;
+
+        if (vc->vc_uni_screen)
+                return 0;
+
+        uniscr = vc_uniscr_alloc(vc->vc_cols, vc->vc_rows);
+        if (!uniscr)
+                return -ENOMEM;
+
+        /*
+         * Let's populate it initially with (imperfect) reverse translation.
+         * This is the next best thing we can do short of having it enabled
+         * from the start even when no users rely on this functionality. True
+         * unicode content will be available after a complete screen refresh.
+         */
+        p = (unsigned short *)vc->vc_origin;
+        mask = vc->vc_hi_font_mask | 0xff;
+        for (y = 0; y < vc->vc_rows; y++) {
+                char32_t *line = uniscr->lines[y];
+                for (x = 0; x < vc->vc_cols; x++) {
+                        u16 glyph = scr_readw(p++) & mask;
+                        line[x] = inverse_translate(vc, glyph, true);
+                }
+        }
+
+        vc->vc_uni_screen = uniscr;
+        return 0;
+}
+
+/*
+ * Called from vcs_read() to get the unicode data from the screen.
+ * This must be preceded by a successful call to vc_uniscr_check() once
+ * the console lock has been taken.
+ */
+void vc_uniscr_copy_line(struct vc_data *vc, void *dest,
+                         unsigned int row, unsigned int col, unsigned int nr)
+{
+        struct uni_screen *uniscr = get_vc_uniscr(vc);
+
+        BUG_ON(!uniscr);
+        memcpy(dest, &uniscr->lines[row][col], nr * sizeof(char32_t));
+}
+
 
 static void con_scroll(struct vc_data *vc, unsigned int t, unsigned int b,
                 enum con_scroll dir, unsigned int nr)
diff --git a/include/linux/selection.h b/include/linux/selection.h
index 5b278ce99d8d..2b34df9f1e26 100644
--- a/include/linux/selection.h
+++ b/include/linux/selection.h
@@ -42,4 +42,9 @@ extern u16 vcs_scr_readw(struct vc_data *vc, const u16 *org);
 extern void vcs_scr_writew(struct vc_data *vc, u16 val, u16 *org);
 extern void vcs_scr_updated(struct vc_data *vc);
 
+extern int vc_uniscr_check(struct vc_data *vc);
+extern void vc_uniscr_copy_line(struct vc_data *vc, void *dest,
+                                unsigned int row, unsigned int col,
+                                unsigned int nr);
+
 #endif