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Subject[PATCH] serial.c procfs kudzu - discussion
Patch submitted for discussion:

This serial driver patch modifies function line_info() which assembles text
to be read from /proc/tty/driver/serial. For example, the text line for the
COM2 port, which is mapped to I/O space, is as follows:

"1: uart:16550A port:2F8 irq:3 tx:0 rx:0"

The patch corrects handling of ports that are on memory mapped devices.
The unpatched function generates a short text line for such ports because
the I/O port address field is zero on memory mapped ports:

"4: uart:16C950/954 port:0 irq:14"

This is the format used for nonexistent ports. Truly nonexistent ports
always have a port type of "unknown port". kudzu depends on that. The bug
causes the short format to be used for all memory mapped ports which have
known types. The absence of the tx: and rx: fields in the short format
causes kudzu to die during system initialization at the "Checking for new
hardware" step:

S05kudzu: Line 78: 237 Segmentation fault

This is caused by a null-pointer de-reference in kudzu's not-so-robust
parser, when it lemmings off the end of the short line.

This patch adds logic to check both the I/O port field and the I/O memory
base address field to detect the presence of hardware. The patched driver
generates the longer format text for memory mapped ports:

"4: uart:16C950/954 port:C4800000 irq:14 tx:0 rx:0 "

Created on kernel files rev 2.4.19-pre2

Contributor: Ed Vance


1. The patch depends on the I/O port address field and the I/O memory
address field both being zero for unconfigured ports. Anybody know of any
exception corner cases where a port gets partially configured and gives
up with one of these fields left non-zero?

2. The label on the displayed I/O memory address is "port:", just like
an I/O port address. Should it display "iomem:" instead of "port:"?

3. A trailing space has been added to all text lines as a cushion for
kudzu. Should this stay in?

4. Should a bug be turned in against kudzu for the weak parser?

diff -urN -X dontdiff.txt linux-2.4.19-pre2/drivers/char/serial.c
--- linux-2.4.19-pre2/drivers/char/serial.c Sat Mar 2 10:38:11 2002
+++ patched/drivers/char/serial.c Wed Mar 6 14:31:44 2002
@@ -3260,10 +3260,12 @@

ret = sprintf(buf, "%d: uart:%s port:%lX irq:%d",
state->line, uart_config[state->type].name,
- state->port, state->irq);
+ (state->port ? state->port : (long)state->iomem_base),
+ state->irq);

- if (!state->port || (state->type == PORT_UNKNOWN)) {
- ret += sprintf(buf+ret, "\n");
+ if ((!state->port && !state->iomem_base) ||
+ (state->type == PORT_UNKNOWN)) {
+ ret += sprintf(buf+ret, " \n");
return ret;

Ed Vance
Macrolink, Inc. 1500 N. Kellogg Dr Anaheim, CA 92807

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