[PATCH RESEND v7 3/3] console: Add persistent scrollback buffers for all VGA consoles

Manuel Schölling
2016-12-21T16:37:38Z

Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel SchÃ¶lling <manuel.schoelling@gmx.de>
Reviewed-by: Andrey Utkin <andrey_utkin@fastmail.com>
Tested-by: Andrey Utkin <andrey_utkin@fastmail.com>
Tested-by: Adam Borowski <kilobyte@angband.pl>

---
drivers/video/console/Kconfig | 25 +++++++-
drivers/video/console/vgacon.c | 142 ++++++++++++++++++++++++++---------------
2 files changed, 111 insertions(+), 56 deletions(-)

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 38da6e2..c5742d2 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -43,9 +43,28 @@ config VGACON_SOFT_SCROLLBACK_SIZE
range 1 1024
default "64"
help
- Enter the amount of System RAM to allocate for the scrollback
- buffer. Each 64KB will give you approximately 16 80x25
- screenfuls of scrollback buffer
+ Enter the amount of System RAM to allocate for scrollback
+ buffers of VGA consoles. Each 64KB will give you approximately
+ 16 80x25 screenfuls of scrollback buffer.
+
+config VGACON_SOFT_SCROLLBACK_PERSISTENT
+ bool "Persistent Scrollback History for each console"
+ depends on VGACON_SOFT_SCROLLBACK
+ default n
+ help
+ Say Y here if the scrollback history should persist when switching
+ between consoles. Otherwise, the scrollback history will be flushed
+ each time the console is switched.
+
+ This feature might break your tool of choice to flush the scrollback
+ buffer, e.g. clear(1) will work fine but Debian's clear_console(1)
+ will be broken, which might cause security issues.
+ You can use the escape sequence \e[3J instead if this feature is
+ activated.
+
+ Note that a buffer of VGACON_SOFT_SCROLLBACK_SIZE is taken for each
+ created tty device.
+ So if you use a RAM-constrained system, say N here.

config MDA_CONSOLE
depends on !M68K && !PARISC && ISA
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 9a7c2bb..ca23d22 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -162,7 +162,7 @@ static inline void vga_set_mem_top(struct vc_data *c)

#ifdef CONFIG_VGACON_SOFT_SCROLLBACK
/* software scrollback */
-static struct vgacon_scrollback_info {
+struct vgacon_scrollback_info {
void *data;
int tail;
int size;
@@ -171,74 +171,110 @@ static struct vgacon_scrollback_info {
int cur;
int save;
int restore;
-} vgacon_scrollback;
+};
+
+static struct vgacon_scrollback_info *vgacon_scrollback_cur;
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_PERSISTENT
+static struct vgacon_scrollback_info vgacon_scrollbacks[MAX_NR_CONSOLES];
+#else
+static struct vgacon_scrollback_info vgacon_scrollbacks[1];
+#endif

-static void vgacon_scrollback_reset(size_t reset_size)
+static void vgacon_scrollback_reset(int vc_num, size_t reset_size)
{
- if (vgacon_scrollback.data && reset_size > 0)
- memset(vgacon_scrollback.data, 0, reset_size);
+ struct vgacon_scrollback_info *scrollback = &vgacon_scrollbacks[vc_num];
+
+ if (scrollback->data && reset_size > 0)
+ memset(scrollback->data, 0, reset_size);

- vgacon_scrollback.cnt = 0;
- vgacon_scrollback.tail = 0;
- vgacon_scrollback.cur = 0;
+ scrollback->cnt = 0;
+ scrollback->tail = 0;
+ scrollback->cur = 0;
}

-static void vgacon_scrollback_init(int pitch)
+static void vgacon_scrollback_init(int vc_num)
{
- int rows = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024/pitch;
-
- if (vgacon_scrollback.data) {
- vgacon_scrollback.cnt = 0;
- vgacon_scrollback.tail = 0;
- vgacon_scrollback.cur = 0;
- vgacon_scrollback.rows = rows - 1;
- vgacon_scrollback.size = rows * pitch;
+ int pitch = vga_video_num_columns * 2;
+ size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+ int rows = size / pitch;
+ void *data;
+
+ data = kmalloc_array(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE, 1024,
+ GFP_NOWAIT);
+
+ vgacon_scrollbacks[vc_num].data = data;
+ vgacon_scrollback_cur = &vgacon_scrollbacks[vc_num];
+
+ vgacon_scrollback_cur->rows = rows - 1;
+ vgacon_scrollback_cur->size = rows * pitch;
+
+ vgacon_scrollback_reset(vc_num, size);
+}
+
+static void vgacon_scrollback_switch(int vc_num)
+{
+#ifndef CONFIG_VGACON_SOFT_SCROLLBACK_PERSISTENT
+ vc_num = 0;
+#endif
+
+ if (!vgacon_scrollbacks[vc_num].data) {
+ vgacon_scrollback_init(vc_num);
+ } else {
+#ifdef CONFIG_VGACON_SOFT_SCROLLBACK_PERSISTENT
+ vgacon_scrollback_cur = &vgacon_scrollbacks[vc_num];
+#else
+ size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;
+
+ vgacon_scrollback_reset(vc_num, size);
+#endif
}
}

static void vgacon_scrollback_startup(void)
{
- vgacon_scrollback.data = kcalloc(CONFIG_VGACON_SOFT_SCROLLBACK_SIZE,
- 1024, GFP_NOWAIT);
- vgacon_scrollback_init(vga_video_num_columns * 2);
+ vgacon_scrollback_cur = &vgacon_scrollbacks[0];
+ vgacon_scrollback_init(0);
}

static void vgacon_scrollback_update(struct vc_data *c, int t, int count)
{
void *p;

- if (!vgacon_scrollback.size || c->vc_num != fg_console)
+ if (!vgacon_scrollback_cur->data || !vgacon_scrollback_cur->size ||
+ c->vc_num != fg_console)
return;

p = (void *) (c->vc_origin + t * c->vc_size_row);

while (count--) {
- scr_memcpyw(vgacon_scrollback.data + vgacon_scrollback.tail,
+ scr_memcpyw(vgacon_scrollback_cur->data +
+ vgacon_scrollback_cur->tail,
p, c->vc_size_row);
- vgacon_scrollback.cnt++;
+
+ vgacon_scrollback_cur->cnt++;
p += c->vc_size_row;
- vgacon_scrollback.tail += c->vc_size_row;
+ vgacon_scrollback_cur->tail += c->vc_size_row;

- if (vgacon_scrollback.tail >= vgacon_scrollback.size)
- vgacon_scrollback.tail = 0;
+ if (vgacon_scrollback_cur->tail >= vgacon_scrollback_cur->size)
+ vgacon_scrollback_cur->tail = 0;

- if (vgacon_scrollback.cnt > vgacon_scrollback.rows)
- vgacon_scrollback.cnt = vgacon_scrollback.rows;
+ if (vgacon_scrollback_cur->cnt > vgacon_scrollback_cur->rows)
+ vgacon_scrollback_cur->cnt = vgacon_scrollback_cur->rows;

- vgacon_scrollback.cur = vgacon_scrollback.cnt;
+ vgacon_scrollback_cur->cur = vgacon_scrollback_cur->cnt;
}
}

static void vgacon_restore_screen(struct vc_data *c)
{
- vgacon_scrollback.save = 0;
+ vgacon_scrollback_cur->save = 0;

- if (!vga_is_gfx && !vgacon_scrollback.restore) {
+ if (!vga_is_gfx && !vgacon_scrollback_cur->restore) {
scr_memcpyw((u16 *) c->vc_origin, (u16 *) c->vc_screenbuf,
c->vc_screenbuf_size > vga_vram_size ?
vga_vram_size : c->vc_screenbuf_size);
- vgacon_scrollback.restore = 1;
- vgacon_scrollback.cur = vgacon_scrollback.cnt;
+ vgacon_scrollback_cur->restore = 1;
+ vgacon_scrollback_cur->cur = vgacon_scrollback_cur->cnt;
}
}

@@ -252,41 +288,41 @@ static void vgacon_scrolldelta(struct vc_data *c, int lines)
return;
}

- if (!vgacon_scrollback.data)
+ if (!vgacon_scrollback_cur->data)
return;

- if (!vgacon_scrollback.save) {
+ if (!vgacon_scrollback_cur->save) {
vgacon_cursor(c, CM_ERASE);
vgacon_save_screen(c);
- vgacon_scrollback.save = 1;
+ vgacon_scrollback_cur->save = 1;
}

- vgacon_scrollback.restore = 0;
- start = vgacon_scrollback.cur + lines;
+ vgacon_scrollback_cur->restore = 0;
+ start = vgacon_scrollback_cur->cur + lines;
end = start + abs(lines);

if (start < 0)
start = 0;

- if (start > vgacon_scrollback.cnt)
- start = vgacon_scrollback.cnt;
+ if (start > vgacon_scrollback_cur->cnt)
+ start = vgacon_scrollback_cur->cnt;

if (end < 0)
end = 0;

- if (end > vgacon_scrollback.cnt)
- end = vgacon_scrollback.cnt;
+ if (end > vgacon_scrollback_cur->cnt)
+ end = vgacon_scrollback_cur->cnt;

- vgacon_scrollback.cur = start;
+ vgacon_scrollback_cur->cur = start;
count = end - start;
- soff = vgacon_scrollback.tail - ((vgacon_scrollback.cnt - end) *
- c->vc_size_row);
+ soff = vgacon_scrollback_cur->tail -
+ ((vgacon_scrollback_cur->cnt - end) * c->vc_size_row);
soff -= count * c->vc_size_row;

if (soff < 0)
- soff += vgacon_scrollback.size;
+ soff += vgacon_scrollback_cur->size;

- count = vgacon_scrollback.cnt - start;
+ count = vgacon_scrollback_cur->cnt - start;

if (count > c->vc_rows)
count = c->vc_rows;
@@ -300,13 +336,13 @@ static void vgacon_scrolldelta(struct vc_data *c, int lines)

count *= c->vc_size_row;
/* how much memory to end of buffer left? */
- copysize = min(count, vgacon_scrollback.size - soff);
- scr_memcpyw(d, vgacon_scrollback.data + soff, copysize);
+ copysize = min(count, vgacon_scrollback_cur->size - soff);
+ scr_memcpyw(d, vgacon_scrollback_cur->data + soff, copysize);
d += copysize;
count -= copysize;

if (count) {
- scr_memcpyw(d, vgacon_scrollback.data, count);
+ scr_memcpyw(d, vgacon_scrollback_cur->data, count);
d += count;
}

@@ -320,13 +356,13 @@ static void vgacon_flush_scrollback(struct vc_data *c)
{
size_t size = CONFIG_VGACON_SOFT_SCROLLBACK_SIZE * 1024;

- if (c->vc_num = fg_console)
- vgacon_scrollback_reset(size);
+ vgacon_scrollback_reset(c->vc_num, size);
}
#else
#define vgacon_scrollback_startup(...) do { } while (0)
#define vgacon_scrollback_init(...) do { } while (0)
#define vgacon_scrollback_update(...) do { } while (0)
+#define vgacon_scrollback_switch(...) do { } while (0)

static void vgacon_restore_screen(struct vc_data *c)
{
@@ -805,7 +841,7 @@ static int vgacon_switch(struct vc_data *c)
vgacon_doresize(c, c->vc_cols, c->vc_rows);
}

- vgacon_scrollback_init(c->vc_size_row);
+ vgacon_scrollback_switch(c->vc_num);
return 0; /* Redrawing not needed */
}

--
2.1.4