--- linux-2.4.19/drivers/char/serial.c Fri Oct 11 15:51:36 2002
+++ linux-2.4.20-pre8/drivers/char/serial.c Fri Oct 11 15:47:27 2002
@@ -62,10 +62,16 @@
* Robert Schwebel <robert@schwebel.de>,
* Juergen Beisert <jbeisert@eurodsn.de>,
* Theodore Ts'o <tytso@mit.edu>
+ *
+ * 10/02: Fixed flow control (CTS) bugs in serial console by adding
+ * status control (DSR, DCD) too. This required new heirarchy of
+ * serial console output functions. Added statistics so users
+ * can debug lack of console output. Incremented to version 5.05d.
+ * Glen Turner <glen.turner+linux@aarnet.edu.au>
*/
-static char *serial_version = "5.05c";
-static char *serial_revdate = "2001-07-08";
+static char *serial_version = "5.05d";
+static char *serial_revdate = "2002-10-11";
/*
* Serial driver configuration section. Here are the various options:
@@ -97,8 +103,10 @@
* ACPI 2.0.
*/
+#include <limits.h> /* For INT_MAX */
#include <linux/config.h>
#include <linux/version.h>
+#include <linux/sysctl.h>
#undef SERIAL_PARANOIA_CHECK
#define CONFIG_SERIAL_NOPAUSE_IO
@@ -248,6 +256,10 @@
#define _INLINE_
#endif
+#ifdef CONFIG_SERIAL_CONSOLE
+static int __init serial_console_sysctl_init(void);
+#endif
+
static char *serial_name = "Serial driver";
static DECLARE_TASK_QUEUE(tq_serial);
@@ -5543,6 +5555,9 @@
#ifdef ENABLE_SERIAL_PNP
probe_serial_pnp();
#endif
+#ifdef CONFIG_SERIAL_CONSOLE
+ serial_console_sysctl_init();
+#endif
return 0;
}
@@ -5778,80 +5793,369 @@
* ------------------------------------------------------------
* Serial console driver
* ------------------------------------------------------------
+ *
+ * When flow control is enabled there are some changes between this
+ * code and v5.05c to fix the following pathological conditions:
+ *
+ * - Linux took upwards of 30 minutes to boot when CTS was never
+ * asserted, such as when a modem or terminal server was idle. This
+ * code checks the DSR and DCD status lines, detecting most cases
+ * where CTS will never be asserted if the terminal server or modem is
+ * configured with status and flow control (AT &C1 &D2 &K3).
+ *
+ * - An attached smart modem would not answer calls during disk
+ * failures. Hayes AT command modems hang up when a call is
+ * negotiating and a character is receieved from the local machine.
+ * So a stream of constant console mesasges, such as from a failing
+ * disk, would never allow the modem to complete negotiation on an
+ * incoming call. This condition can be avoided if the kernel flow
+ * control code checks the DCD status line and the modem is configured
+ * to assert DCD upon the conclusion of call negotiation (AT &C1).
+ *
+ * and the following bugs:
+ *
+ * - Security consideration: kernel messages, possibly containing
+ * user-derived text, were sent to modems without active calls. Smart
+ * modems without active calls are in command mode. So users had a
+ * path to subvert modem configurations (eg: alter auto-answer,
+ * callback or authentication). This bug exists without the flow
+ * control option, but can't be fixed without looking at the status
+ * lines (implying that the flow control option is a Good Idea for
+ * security-conscious sites).
+ *
+ * - When CTS timed out v5.05c send the character regardless. If CTS
+ * is used for media access control, such as on a multi-drop line or
+ * satelite circuit, other users of the circuit would be disrupted.
+ *
+ * - When the Transmit Buffer timed out v5.05 queued the character
+ * regardless. This could result in a number of the issues above.
+ *
+ * The behaviour *without* flow control remains identical to v5.05c,
+ * with the exception of Transmit Buffer timeouts. These now cause the
+ * message to be discarded (and counted).
+ *
+ * In short, professional RS-232 applications should configure the
+ * flow control option and supply strictly correct status (DSR, DCD)
+ * and flow control (CTS) signals. For example:
+ *
+ * console=ttyS0,9600n8r
+ *
+ * A quick three-wire hack to grab an Oops message should not use flow
+ * control. For example:
+ *
+ * console=ttyS0,9600n8
*/
#ifdef CONFIG_SERIAL_CONSOLE
-#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
-
static struct async_struct async_sercons;
+/* A count of the number of messages, dropped messages and reasons for
+ * dropping messages. There really should be one of these for each
+ * console=ttyS parameter. The counters are not yet visible to user
+ * space.
+ */
+static struct serial_console_counters_t serial_console_counters;
+
+/* Maximum number of times to test for an empty transmit buffer.
+ * About 1S. Can be tuned using dev.serialconsole.timeout-transmit.
+ * This number could be significantly smaller than 1M, as even at
+ * 75bps the tramsit buffer of contemporary UARTs will clear in 0.5S.
+ */
+static int serial_console_attempts_tx = 1000000;
+/* Maximum number of times to test for CTS to be asserted when using
+ * flow control. About 1S. Can be tuned using
+ * dev.serialconsole.timeout-cts.
+ */
+static int serial_console_attempts_cts = 1000000;
-/*
- * Wait for transmitter & holding register to empty
+
+/* Sysctl routines to access serial_console_counters.
+ *
+ * See "sysctl interface" in linux/Docmentaion/DocBook/kernel-api.*
*/
-static inline void wait_for_xmitr(struct async_struct *info)
+static int serial_console_attempts_min = 1;
+static int serial_console_attempts_max = INT_MAX;
+static ctl_table serial_console_sysctl_files[] = {
+ { 1, "messages-total",
+ &(serial_console_counters.messages_total), sizeof(int),
+ 0444, NULL,
+ &proc_dointvec },
+ { 2, "messages-dropped",
+ &(serial_console_counters.messages_dropped), sizeof(int),
+ 0444, NULL,
+ &proc_dointvec },
+ { 3, "timeouts-transmit",
+ &(serial_console_counters.timeouts_tx), sizeof(int),
+ 0444, NULL,
+ &proc_dointvec },
+ { 4, "timeouts-data-set-ready",
+ &(serial_console_counters.timeouts_dsr), sizeof(int),
+ 0444, NULL,
+ &proc_dointvec },
+ { 5, "timeouts-data-carrier-detect",
+ &(serial_console_counters.timeouts_cts), sizeof(int),
+ 0444, NULL,
+ &proc_dointvec },
+ { 6, "timeouts-clear-to-send",
+ &(serial_console_counters.timeouts_cts), sizeof(int),
+ 0444, NULL,
+ &proc_dointvec },
+ { 7, "maximum-attempts-transmit",
+ &serial_console_attempts_tx, sizeof(int),
+ 0664, NULL,
+ &proc_dointvec_minmax, NULL, NULL,
+ &serial_console_attempts_min,
+ &serial_console_attempts_max },
+ { 8, "maximum-attempts-clear-to-send",
+ &serial_console_attempts_cts, sizeof(int),
+ 0664, NULL,
+ &proc_dointvec_minmax, NULL, NULL,
+ &serial_console_attempts_min,
+ &serial_console_attempts_max },
+ { 0 } /* Last */
+};
+
+static ctl_table serial_console_sysctl_directory[] = {
+ { 1, "serialconsole",
+ NULL, 0,
+ 0555, serial_console_sysctl_files },
+ { 0 } /* Last */
+};
+
+static ctl_table serial_console_sysctl_root[] = {
+ { CTL_DEV, "dev",
+ NULL, 0,
+ 0555, serial_console_sysctl_directory },
+ { 0 } /* Last */
+};
+
+static struct ctl_table_header *serial_console_sysctl;
+
+
+/* Initialise statitsics for the serial console.
+ *
+ * Called from rs_init(), the serial device initialiser. Calling this
+ * routine from serial_console_init() leads to an Oops, perhaps the
+ * necessary infrastructure is not in place at that time. Hmmm. -GDT
+ *
+ * Returns: 0, always.
+ */
+static int __init serial_console_sysctl_init(void)
+{
+ memset(&serial_console_counters,
+ 0,
+ sizeof(serial_console_counters));
+ serial_console_sysctl =
+ register_sysctl_table(serial_console_sysctl_root,
+ 0); /* Insert at end */
+ return 0;
+}
+
+
+/* There is no
+ * static void __exit serial_console_sysctl_exit(void)
+ * as compling this code as a MODULE defeats CONFIG_SERIAL_CONSOLE.
+ * This should be added should Alan Cox succeed in making all code
+ * module-based.
+ */
+
+
+/* Wait for UART's transmitter queue to empty.
+ *
+ * Inputs: info -- RS232 port used as console.
+ * Returns: 0 -- the waiting character can be transmitted
+ * non-0 -- discard message to be transmitted, as the
+ * transmit queue is massively long or stuck.
+ * Globals: serial_console_counters.
+ */
+#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
+
+static inline int serial_console_drain(struct async_struct *info)
{
- unsigned int status, tmout = 1000000;
+ /* Number of times to test the transmit buffer of the UART. */
+ unsigned int timeout;
+ /* Contents of a UART status register. */
+ unsigned int status;
+ timeout = serial_console_attempts_tx;
+ /* Drain transmit buffer. */
do {
status = serial_in(info, UART_LSR);
- if (status & UART_LSR_BI)
+ /* If Break has been recieved then note that for the
+ * regular user of the serial port.
+ */
+ if (status & UART_LSR_BI) {
lsr_break_flag = UART_LSR_BI;
+ }
- if (--tmout == 0)
- break;
- } while((status & BOTH_EMPTY) != BOTH_EMPTY);
+ if (--timeout == 0) {
+ /* Transmit buffer hasn't emptied in a
+ * reasonable time. Discard the character.
+ */
+ serial_console_counters.timeouts_tx++;
+ return (info->flags & ASYNC_CONS_FLOW);
+ }
+ } while ((status & BOTH_EMPTY) != BOTH_EMPTY);
+ return 0;
+}
+
+/* Wait for transmitter queue to empty. If using flow control then
+ * check if RS-232 status signals are asserted and wait for flow
+ * control to be asserted.
+ *
+ *
+ * Inputs: info -- RS232 port used as console.
+ * Returns: 0 -- the waiting character can be transmitted
+ * non-0 -- discard message to be transmitted, usually because
+ * RS-232 status control lines indicate no reciever.
+ * Globals: lsr_break_flag -- updated if RS-232 Break condition reported.
+ * serial_console_counters
+ */
+static inline int serial_console_flow(struct async_struct *info)
+{
+ /* Timeout loop tests Clear to Send. */
+ unsigned int timeout;
+ /* Contents of a UART status register. */
+ unsigned int status;
- /* Wait for flow control if necessary */
+ if (serial_console_drain(info))
+ {
+ return !0;
+ }
+
+ /* If flow control is configured then wait for Clear to Send
+ * to be asserted. Abandon message if no status lines
+ * asserted.
+ */
if (info->flags & ASYNC_CONS_FLOW) {
- tmout = 1000000;
- while (--tmout &&
- ((serial_in(info, UART_MSR) & UART_MSR_CTS) == 0));
- }
-}
+ for (timeout = serial_console_attempts_cts;
+ timeout > 0;
+ timeout --) {
+ status = serial_in(info, UART_MSR);
+ /* None of the modem status lines, including
+ * Clear to Send, are valid unless Data Set
+ * Ready is asserted. Also, we should not
+ * transmit unless Data Carrier Detect is
+ * asserted (implying that a receiver is
+ * present). If DSR or DCD is not present we
+ * discard the message (the carrier won't be
+ * asserted in the time taken to poll the UART
+ * a few times more). Distinct DSR and DCD
+ * counters are maintained for simple
+ * diagnosis of cable and modem faults.
+ */
+ if ((status & UART_MSR_DSR) == 0) {
+ serial_console_counters.timeouts_dsr++;
+ return !0;
+ }
+ if ((status & UART_MSR_DCD) == 0) {
+ serial_console_counters.timeouts_dcd++;
+ return !0;
+ }
+ /* At this point DSR and DCD are asserted, so
+ * valid to test flow control.
+ */
+ if (status & UART_MSR_CTS) {
+ return 0;
+ }
+ }
+ /* CTS still not asserted. Discard the message for
+ * correct operation on multi-drop lines.
+ */
+ serial_console_counters.timeouts_cts++;
+ return !0;
+ }
+ return 0;
+}
-/*
- * Print a string to the serial port trying not to disturb
- * any possible real use of the port...
+/* Print 'ch' to the serial console at 'info'.
*
- * The console must be locked when we get here.
+ * Inputs: info -- RS232 port used as console.
+ * ch -- character to print.
+ * Returns: 0 -- 'ch' was transmitted, caller should send me more
+ * characters of the message.
+ * non-0 -- 'ch' was dropped, caller should discard remainder
+ * of message.
*/
-static void serial_console_write(struct console *co, const char *s,
- unsigned count)
+static int serial_console_out(struct async_struct *info,
+ char ch)
+{
+ int error;
+
+ error = serial_console_flow(info);
+ if (!error) {
+ serial_out(info, UART_TX, ch);
+ }
+ return error;
+}
+
+/* Print a string 'message' of 'message_length' to the serial
+ * port. 'co' is ingnored, as the serial console is described by the
+ * global 'async_sercons'.
+ *
+ * Try not to disturb any possible real use of the port (such as by
+ * getty). So use polling rather than interrupts.
+ *
+ * The console must be locked when we get here.
+ *
+ * Inputs: co -- console to print message upon, ignored.
+ * message -- pointer to text to print.
+ * message_length -- amount of text, [0, MAX_UINT].
+ * Globals: async_sercons.
+ */
+static void serial_console_write(struct console *co,
+ const char *message,
+ unsigned int message_length)
{
static struct async_struct *info = &async_sercons;
- int ier;
- unsigned i;
+ unsigned int ier;
+ /* We go to some trouble with unsigned ints and avoiding array
+ * references to ensure that messages can be longer than is
+ * indexable by an int/size_t. Not sure why the ability to
+ * print 4 billion characters is valuable, unless we're trying
+ * to avoid invalid memory accesses upon corrupt
+ * message_lengths [GDT].
+ */
+ unsigned int u;
+ const char *p;
- /*
- * First save the IER then disable the interrupts
+ serial_console_counters.messages_total++;
+
+ /* Salt away the serial port UART's Interrupt Enable Register
+ * before disabling UART interrupts.
*/
ier = serial_in(info, UART_IER);
serial_out(info, UART_IER, 0x00);
- /*
- * Now, do each character
- */
- for (i = 0; i < count; i++, s++) {
- wait_for_xmitr(info);
-
- /*
- * Send the character out.
- * If a LF, also do CR...
- */
- serial_out(info, UART_TX, *s);
- if (*s == 10) {
- wait_for_xmitr(info);
- serial_out(info, UART_TX, 13);
+ /* Send each character down the port. */
+ for (u = 0, p = message; u < message_length; u++, p++)
+ {
+ if (*p == '\n') {
+ /* Expand end of line LF to CR LF, as expected
+ * by terminals and printers. v5.05c sent LF
+ * CR, which isn't right for printers.
+ */
+ if (serial_console_out(info, '\r')) {
+ serial_console_counters.messages_dropped++;
+ break;
+ }
+ }
+ if (serial_console_out(info, *p)) {
+ serial_console_counters.messages_dropped++;
+ break;
}
}
+ /* At this point all characters are sent or we have abandoned
+ * the message due to soft errors like timeouts on transmit
+ * queues, timeouts on CTS or unasserted DSR or DCD.
+ */
- /*
- * Finally, Wait for transmitter & holding register to empty
- * and restore the IER
+ /* Restore the interrupt status. v5.05c also waited up to 1S
+ * for any flow control to be reasserted, now we leave any
+ * user application to cope with that.
*/
- wait_for_xmitr(info);
+ (void)serial_console_drain(info);
serial_out(info, UART_IER, ier);
}
-
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This archive was generated by hypermail 2b29 : Tue Oct 15 2002 - 22:00:48 EST