strip.c

讲述linux的初始化过程

                /* else, another different byte, so add it to the block */
                else
                {
                    *dst++ = *src ^ Stuff_Magic;
                    count++;
                }
                src++;    /* Consume the byte */
                break;
        }
        if (count == Stuff_MaxCount)
        {
            StuffData_FinishBlock(code + count);
        }
    }
    if (code == Stuff_NoCode)
    {
        *code_ptr_ptr = NULL;
    }
    else
    {
        *code_ptr_ptr = code_ptr;
        StuffData_FinishBlock(code + count);
    }
    return(dst);
}

/*
 * UnStuffData decodes the data at "src", up to (but not including) "end".
 * It writes the decoded data into the buffer pointed to by "dst", up to a
 * maximum of "dst_length", and returns the new value of "src" so that a
 * follow-on call can read more data, continuing from where the first left off.
 * 
 * There are three types of results:
 * 1. The source data runs out before extracting "dst_length" bytes:
 *    UnStuffData returns NULL to indicate failure.
 * 2. The source data produces exactly "dst_length" bytes:
 *    UnStuffData returns new_src = end to indicate that all bytes were consumed.
 * 3. "dst_length" bytes are extracted, with more remaining.
 *    UnStuffData returns new_src < end to indicate that there are more bytes
 *    to be read.
 * 
 * Note: The decoding may be destructive, in that it may alter the source
 * data in the process of decoding it (this is necessary to allow a follow-on
 * call to resume correctly).
 */

static __u8 *UnStuffData(__u8 *src, __u8 *end, __u8 *dst, __u32 dst_length)
{
    __u8 *dst_end = dst + dst_length;
    /* Sanity check */
    if (!src || !end || !dst || !dst_length)
        return(NULL);
    while (src < end && dst < dst_end)
    {
        int count = (*src ^ Stuff_Magic) & Stuff_CountMask;
        switch ((*src ^ Stuff_Magic) & Stuff_CodeMask)
        {
            case Stuff_Diff:
                if (src+1+count >= end)
                    return(NULL);
                do
                {
                    *dst++ = *++src ^ Stuff_Magic;
                }
                while(--count >= 0 && dst < dst_end);
                if (count < 0)
                    src += 1;
                else
                {
                    if (count == 0)
                        *src = Stuff_Same ^ Stuff_Magic;
                    else
                        *src = (Stuff_Diff + count) ^ Stuff_Magic;
                }
                break;
            case Stuff_DiffZero:
                if (src+1+count >= end)
                    return(NULL);
                do
                {
                    *dst++ = *++src ^ Stuff_Magic;
                }
                while(--count >= 0 && dst < dst_end);
                if (count < 0)
                    *src = Stuff_Zero ^ Stuff_Magic;
                else
                    *src = (Stuff_DiffZero + count) ^ Stuff_Magic;
                break;
            case Stuff_Same:
                if (src+1 >= end)
                    return(NULL);
                do
                {
                    *dst++ = src[1] ^ Stuff_Magic;
                }
                while(--count >= 0 && dst < dst_end);
                if (count < 0)
                    src += 2;
                else
                    *src = (Stuff_Same + count) ^ Stuff_Magic;
                break;
            case Stuff_Zero:
                do
                {
                    *dst++ = 0;
                }
                while(--count >= 0 && dst < dst_end);
                if (count < 0)
                    src += 1;
                else
                    *src = (Stuff_Zero + count) ^ Stuff_Magic;
                break;
        }
    }
    if (dst < dst_end)
        return(NULL);
    else
        return(src);
}


/************************************************************************/
/* General routines for STRIP						*/

/*
 * get_baud returns the current baud rate, as one of the constants defined in
 * termbits.h
 * If the user has issued a baud rate override using the 'setserial' command
 * and the logical current rate is set to 38.4, then the true baud rate
 * currently in effect (57.6 or 115.2) is returned.
 */
static unsigned int get_baud(struct tty_struct *tty)
    {
    if (!tty || !tty->termios) return(0);
    if ((tty->termios->c_cflag & CBAUD) == B38400 && tty->driver_data)
        {
        struct async_struct *info = (struct async_struct *)tty->driver_data;
        if ((info->flags & ASYNC_SPD_MASK) == ASYNC_SPD_HI ) return(B57600);
        if ((info->flags & ASYNC_SPD_MASK) == ASYNC_SPD_VHI) return(B115200);
        }
    return(tty->termios->c_cflag & CBAUD);
    }

/*
 * set_baud sets the baud rate to the rate defined by baudcode
 * Note: The rate B38400 should be avoided, because the user may have
 * issued a 'setserial' speed override to map that to a different speed.
 * We could achieve a true rate of 38400 if we needed to by cancelling
 * any user speed override that is in place, but that might annoy the
 * user, so it is simplest to just avoid using 38400.
 */
static void set_baud(struct tty_struct *tty, unsigned int baudcode)
    {
    struct termios old_termios = *(tty->termios);
    tty->termios->c_cflag &= ~CBAUD; /* Clear the old baud setting */
    tty->termios->c_cflag |= baudcode; /* Set the new baud setting */
    tty->driver.set_termios(tty, &old_termios);
    }

/*
 * Convert a string to a Metricom Address.
 */

#define IS_RADIO_ADDRESS(p) (                                                 \
  isdigit((p)[0]) && isdigit((p)[1]) && isdigit((p)[2]) && isdigit((p)[3]) && \
  (p)[4] == '-' &&                                                            \
  isdigit((p)[5]) && isdigit((p)[6]) && isdigit((p)[7]) && isdigit((p)[8])    )

static int string_to_radio_address(MetricomAddress *addr, __u8 *p)
{
    if (!IS_RADIO_ADDRESS(p)) return(1);
    addr->c[0] = 0;
    addr->c[1] = 0;
    addr->c[2] = READHEX(p[0]) << 4 | READHEX(p[1]);
    addr->c[3] = READHEX(p[2]) << 4 | READHEX(p[3]);
    addr->c[4] = READHEX(p[5]) << 4 | READHEX(p[6]);
    addr->c[5] = READHEX(p[7]) << 4 | READHEX(p[8]);
    return(0);
}

/*
 * Convert a Metricom Address to a string.
 */

static __u8 *radio_address_to_string(const MetricomAddress *addr, MetricomAddressString *p)
{
    sprintf(p->c, "%02X%02X-%02X%02X", addr->c[2], addr->c[3], addr->c[4], addr->c[5]);
    return(p->c);
}

/*
 * Note: Must make sure sx_size is big enough to receive a stuffed
 * MAX_RECV_MTU packet. Additionally, we also want to ensure that it's
 * big enough to receive a large radio neighbour list (currently 4K).
 */

static int allocate_buffers(struct strip *strip_info)
{
    struct net_device *dev = &strip_info->dev;
    int sx_size    = MAX(STRIP_ENCAP_SIZE(MAX_RECV_MTU), 4096);
    int tx_size    = STRIP_ENCAP_SIZE(dev->mtu) + MaxCommandStringLength;
    __u8 *r = kmalloc(MAX_RECV_MTU, GFP_ATOMIC);
    __u8 *s = kmalloc(sx_size,      GFP_ATOMIC);
    __u8 *t = kmalloc(tx_size,      GFP_ATOMIC);
    if (r && s && t)
    {
        strip_info->rx_buff = r;
        strip_info->sx_buff = s;
        strip_info->tx_buff = t;
        strip_info->sx_size = sx_size;
        strip_info->tx_size = tx_size;
        strip_info->mtu     = dev->mtu;
        return(1);
    }
    if (r) kfree(r);
    if (s) kfree(s);
    if (t) kfree(t);
    return(0);
}

/*
 * MTU has been changed by the IP layer. Unfortunately we are not told
 * about this, but we spot it ourselves and fix things up. We could be in
 * an upcall from the tty driver, or in an ip packet queue.
 */

static void strip_changedmtu(struct strip *strip_info)
{
    int old_mtu           = strip_info->mtu;
    struct net_device *dev    = &strip_info->dev;
    unsigned char *orbuff = strip_info->rx_buff;
    unsigned char *osbuff = strip_info->sx_buff;
    unsigned char *otbuff = strip_info->tx_buff;
    InterruptStatus intstat;

    if (dev->mtu > MAX_SEND_MTU)
    {
        printk(KERN_ERR "%s: MTU exceeds maximum allowable (%d), MTU change cancelled.\n",
            strip_info->dev.name, MAX_SEND_MTU);
        dev->mtu = old_mtu;
        return;
    }

    /*
     * Have to disable interrupts here because we're reallocating and resizing
     * the serial buffers, and we can't have data arriving in them while we're
     * moving them around in memory. This may cause data to be lost on the serial
     * port, but hopefully people won't change MTU that often.
     * Also note, this may not work on a symmetric multi-processor system.
     */
    intstat = DisableInterrupts();

    if (!allocate_buffers(strip_info))
    {
        RestoreInterrupts(intstat);
        printk(KERN_ERR "%s: unable to grow strip buffers, MTU change cancelled.\n",
            strip_info->dev.name);
        dev->mtu = old_mtu;
        return;
    }

    if (strip_info->sx_count)
    {
        if (strip_info->sx_count <= strip_info->sx_size)
            memcpy(strip_info->sx_buff, osbuff, strip_info->sx_count);
        else
        {
            strip_info->discard = strip_info->sx_count;
            strip_info->rx_over_errors++;
        }
    }

    if (strip_info->tx_left)
    {
        if (strip_info->tx_left <= strip_info->tx_size)
            memcpy(strip_info->tx_buff, strip_info->tx_head, strip_info->tx_left);
        else
        {
            strip_info->tx_left = 0;
            strip_info->tx_dropped++;
        }
    }
    strip_info->tx_head = strip_info->tx_buff;

    RestoreInterrupts(intstat);

    printk(KERN_NOTICE "%s: strip MTU changed fom %d to %d.\n",
        strip_info->dev.name, old_mtu, strip_info->mtu);

    if (orbuff) kfree(orbuff);
    if (osbuff) kfree(osbuff);
    if (otbuff) kfree(otbuff);
}

static void strip_unlock(struct strip *strip_info)
{
    /*
     * Set the timer to go off in one second.
     */
    strip_info->idle_timer.expires = jiffies + 1*HZ;
    add_timer(&strip_info->idle_timer);
    netif_wake_queue(&strip_info->dev);
}


/************************************************************************/
/* Callback routines for exporting information through /proc		*/

/*
 * This function updates the total amount of data printed so far. It then
 * determines if the amount of data printed into a buffer  has reached the
 * offset requested. If it hasn't, then the buffer is shifted over so that
 * the next bit of data can be printed over the old bit. If the total
 * amount printed so far exceeds the total amount requested, then this
 * function returns 1, otherwise 0.
 */
static int 
shift_buffer(char *buffer, int requested_offset, int requested_len,
             int *total, int *slop, char **buf)
{
    int printed;

    /* printk(KERN_DEBUG "shift: buffer: %d o: %d l: %d t: %d buf: %d\n",
           (int) buffer, requested_offset, requested_len, *total,
           (int) *buf); */
    printed = *buf - buffer;
    if (*total + printed <= requested_offset) {
        *total += printed;
        *buf = buffer;
    }
    else {
        if (*total < requested_offset) {
            *slop = requested_offset - *total;
        }
        *total = requested_offset + printed - *slop;
    }
    if (*total > requested_offset + requested_len) {
        return 1;
    }
    else {
        return 0;
    }
}

/*
 * This function calculates the actual start of the requested data
 * in the buffer. It also calculates actual length of data returned,
 * which could be less that the amount of data requested.
 */
static int
calc_start_len(char *buffer, char **start, int requested_offset,
               int requested_len, int total, char *buf)
{
    int return_len, buffer_len;

    buffer_len = buf - buffer;
    if (buffer_len >= 4095) {
 	printk(KERN_ERR "STRIP: exceeded /proc buffer size\n");
    }

    /*
     * There may be bytes before and after the
     * chunk that was actually requested.
     */
    return_len = total - requested_offset;
    if (return_len < 0) {
        return_len = 0;
    }