Linux/NetDriver/sheep_net.c

/*
 *  sheep_net.c - Linux driver for SheepShaver/Basilisk II networking (access to raw Ethernet packets)
 *
 *  sheep_net (C) 1999 Mar"c" Hellwig and Christian Bauer
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/version.h>
#include <linux/miscdevice.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/if_ether.h>
#include <linux/if_arp.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <net/sock.h>
#include <asm/uaccess.h>

#define DEBUG 0

#define bug printk
#if DEBUG
#define D(x) (x);
#else
#define D(x) ;
#endif


// Constants
#define SHEEP_NET_MINOR 198             // Driver minor number
#define MAX_QUEUE 32                    // Maximum number of packets in queue
#define PROT_MAGIC 1520                 // Our "magic" protocol type

// Prototypes
static int sheep_net_open(struct inode *inode, struct file *f);
static int sheep_net_release(struct inode *inode, struct file *f);
static ssize_t sheep_net_read(struct file *f, char *buf, size_t count, loff_t *off);
static ssize_t sheep_net_write(struct file *f, const char *buf, size_t count, loff_t *off);
static unsigned int sheep_net_poll(struct file *f, struct poll_table_struct *wait);
static int sheep_net_ioctl(struct inode *inode, struct file *f, unsigned int code, unsigned long arg);
static int sheep_net_receiver(struct sk_buff *skb, struct device *dev, struct packet_type *pt);


/*
 *  Driver private variables
 */

struct SheepVars {
        struct device *ether;           // The Ethernet device we're attached to
        struct sock *skt;                       // Socket for communication with Ethernet card
        struct sk_buff_head queue;      // Receiver packet queue
        struct packet_type pt;          // Receiver packet type
        struct wait_queue *wait;        // Wait queue for blocking read operations
};


/*
 *  file_operations structure - has function pointers to the
 *  various entry points for device operations
 */

static struct file_operations sheep_net_fops = {
        NULL,   // llseek
        sheep_net_read,
        sheep_net_write,
        NULL,   // readdir
        sheep_net_poll,
        sheep_net_ioctl,
        NULL,   // mmap
        sheep_net_open,
        NULL,   // flush
        sheep_net_release,
        NULL,   // fsync
        NULL,   // fasync
        NULL,   // check_media_change
        NULL,   // revalidate
        NULL    // lock
};


/*
 *  miscdevice structure for driver initialization
 */

static struct miscdevice sheep_net_device = {
        SHEEP_NET_MINOR,        // minor number
        "sheep_net",            // name
        &sheep_net_fops,
        NULL,
        NULL
};


/*
 *  Initialize module
 */

int init_module(void)
{
        int ret;

        // Register driver
        ret = misc_register(&sheep_net_device);
        D(bug("Sheep net driver installed\n"));
        return ret;
}


/*
 *  Deinitialize module
 */

int cleanup_module(void)
{
        int ret;

        // Unregister driver
        ret = misc_deregister(&sheep_net_device);
        D(bug("Sheep net driver removed\n"));
        return ret;
}


/*
 *  Driver open() function
 */

static int sheep_net_open(struct inode *inode, struct file *f)
{
        struct SheepVars *v;
        D(bug("sheep_net: open\n"));

        // Must be opened with read permissions
        if ((f->f_flags & O_ACCMODE) == O_WRONLY)
                return -EPERM;

        // Allocate private variables
        v = (struct SheepVars *)f->private_data = kmalloc(sizeof(struct SheepVars), GFP_USER);
        if (v == NULL)
                return -ENOMEM;
        memset(v, 0, sizeof(struct SheepVars));
        skb_queue_head_init(&v->queue);

        // Yes, we're open
        MOD_INC_USE_COUNT;
        return 0;
}


/*
 *  Driver release() function
 */

static int sheep_net_release(struct inode *inode, struct file *f)
{
        struct SheepVars *v = (struct SheepVars *)f->private_data;
        struct sk_buff *skb;
        D(bug("sheep_net: close\n"));

        // Detach from Ethernet card
        if (v->ether) {
                dev_remove_pack(&v->pt);
                sk_free(v->skt);
                v->skt = NULL;
                v->ether = NULL;
        }

        // Empty packet queue
        while ((skb = skb_dequeue(&v->queue)) != NULL)
                dev_kfree_skb(skb);

        // Free private variables
        kfree(v);

        // Sorry, we're closed
        MOD_DEC_USE_COUNT;
        return 0;
}


/*
 *  Driver read() function
 */

static ssize_t sheep_net_read(struct file *f, char *buf, size_t count, loff_t *off)
{
        struct SheepVars *v = (struct SheepVars *)f->private_data;
        struct sk_buff *skb;
        sigset_t sigs;
        int i;
        D(bug("sheep_net: read\n"));

        for (;;) {

                // Get next packet from queue
                start_bh_atomic();
                skb = skb_dequeue(&v->queue);
                end_bh_atomic();
                if (skb != NULL || (f->f_flags & O_NONBLOCK))
                        break;

                // No packet in queue and in blocking mode, so block
                interruptible_sleep_on(&v->wait);

                // Signal received? Then bail out
                signandsets(&sigs, &current->signal, &current->blocked);
                for (i=0; i<_NSIG_WORDS; i++) {
                        if (sigs.sig[i])
                                return -EINTR;
                }
        }
        if (skb == NULL)
                return -EAGAIN;

        // Pass packet to caller
        if (count > skb->len)
                count = skb->len;
        if (copy_to_user(buf, skb->data, count))
                count = -EFAULT;
        dev_kfree_skb(skb);
        return count;
}


/*
 *  Driver write() function
 */

static ssize_t sheep_net_write(struct file *f, const char *buf, size_t count, loff_t *off)
{
        struct SheepVars *v = (struct SheepVars *)f->private_data;
        struct sk_buff *skb;
        char *p;
        D(bug("sheep_net: write\n"));

        // Check packet size
        if (count < sizeof(struct ethhdr))
                return -EINVAL;
        if (count > 1514)
                count = 1514;

        // Interface active?
        if (v->ether == NULL)
                return count;

        // Allocate buffer for packet
        skb = dev_alloc_skb(count);
        if (skb == NULL)
                return -ENOBUFS;

        // Stuff packet in buffer
        p = skb_put(skb, count);
        if (copy_from_user(p, buf, count)) {
                kfree_skb(skb);
                return -EFAULT;
        }

        // Transmit packet
        dev_lock_list();
        atomic_add(skb->truesize, &v->skt->wmem_alloc);
        skb->sk = v->skt;
        skb->dev = v->ether;
        skb->priority = 0;
        skb->protocol = PROT_MAGIC;     // "Magic" protocol value to recognize our packets in sheep_net_receiver()
        skb->nh.raw = skb->h.raw = skb->data + v->ether->hard_header_len;
        dev_unlock_list();
        dev_queue_xmit(skb);
        return count;
}


/*
 *  Driver poll() function
 */

static unsigned int sheep_net_poll(struct file *f, struct poll_table_struct *wait)
{
        struct SheepVars *v = (struct SheepVars *)f->private_data;
        D(bug("sheep_net: poll\n"));

        // Packets in queue? Then return
        start_bh_atomic();
        if (!skb_queue_empty(&v->queue)) {
                end_bh_atomic();
                return POLLIN | POLLRDNORM;
        }

        // Otherwise wait for packet
        poll_wait(f, &v->wait, wait);
        if (!skb_queue_empty(&v->queue)) {
                end_bh_atomic();
                return POLLIN | POLLRDNORM;
        } else {
                end_bh_atomic();
                return 0;
        }
}


/*
 *  Driver ioctl() function
 */

static int sheep_net_ioctl(struct inode *inode, struct file *f, unsigned int code, unsigned long arg)
{
        struct SheepVars *v = (struct SheepVars *)f->private_data;
        D(bug("sheep_net: ioctl %04x\n", code));

        switch (code) {

                // Attach to Ethernet card
                // arg: pointer to name of Ethernet device (char[8])
                case SIOCSIFLINK: {
                        char name[8];

                        // Already attached?
                        if (v->ether)
                                return -EBUSY;

                        // Get Ethernet card name
                        if (copy_from_user(name, (void *)arg, 8))
                                return -EFAULT;
                        name[7] = 0;

                        // Find card
                        dev_lock_list();
                        v->ether = dev_get(name);
                        if (v->ether == NULL) {
                                dev_unlock_list();
                                return -ENODEV;
                        }

                        // Is it Ethernet?
                        if (v->ether->type != ARPHRD_ETHER) {
                                v->ether = NULL;
                                dev_unlock_list();
                                return -EINVAL;
                        }

                        // Allocate socket
                        v->skt = sk_alloc(0, GFP_USER, 1);
                        if (v->skt == NULL) {
                                v->ether = NULL;
                                dev_unlock_list();
                                return -ENOMEM;
                        }
                        v->skt->dead = 1;

                        // Attach packet handler
                        v->pt.type = htons(ETH_P_ALL);
                        v->pt.dev = v->ether;
                        v->pt.func = sheep_net_receiver;
                        v->pt.data = v;
                        dev_add_pack(&v->pt);
                        dev_unlock_list();
                        return 0;
                }

                // Get hardware address of Ethernet card
                // arg: pointer to buffer (6 bytes) to store address
                case SIOCGIFADDR:
                        if (v->ether == NULL)
                                return -ENODEV;
                        if (copy_to_user((void *)arg, v->ether->dev_addr, 6))
                                return -EFAULT;
                        return 0;

                // Add multicast address
                // arg: pointer to address (6 bytes)
                case SIOCADDMULTI: {
                        char addr[6];
                        if (v->ether == NULL)
                                return -ENODEV;
                        if (copy_from_user(addr, (void *)arg, 6))
                                return -EFAULT;
                        return dev_mc_add(v->ether, addr, 6, 0);
                }

                // Remove multicast address
                // arg: pointer to address (6 bytes)
                case SIOCDELMULTI: {
                        char addr[6];
                        if (v->ether == NULL)
                                return -ENODEV;
                        if (copy_from_user(addr, (void *)arg, 6))
                                return -EFAULT;
                        return dev_mc_delete(v->ether, addr, 6, 0);
                }

                // Return size of first packet in queue
                case FIONREAD: {
                        int count = 0;
                        struct sk_buff *skb;
                        start_bh_atomic();
                        skb = skb_peek(&v->queue);
                        if (skb)
                                count = skb->len;
                        end_bh_atomic();
                        return put_user(count, (int *)arg);
                }

                default:
                        return -ENOIOCTLCMD;
        }
}


/*
 *  Packet receiver function
 */

static int sheep_net_receiver(struct sk_buff *skb, struct device *dev, struct packet_type *pt)
{
        struct SheepVars *v = (struct SheepVars *)pt->data;
        D(bug("sheep_net: packet received\n"));

        // Packet sent by us? Then discard
        if (skb->protocol == PROT_MAGIC) {
                kfree_skb(skb);
                return 0;
        }

        // Discard packets if queue gets too full
        if (skb_queue_len(&v->queue) > MAX_QUEUE) {
                kfree_skb(skb);
                return 0;
        }

        // We also want the Ethernet header
        skb_push(skb, skb->data - skb->mac.raw);

        // Enqueue packet
        start_bh_atomic();
        skb_queue_tail(&v->queue, skb);
        end_bh_atomic();

        // Unblock blocked read
        wake_up(&v->wait);
        return 0;
}
Revision:	1.1
Committed:	1999-10-03T14:16:25Z (25 years, 1 month ago) by cebix
Content type:	text/plain
Branch:	MAIN
Branch point for:	cebix
Log Message:	Initial revision
#	User	Rev	Content
1	cebix	1.1	/*
2			* sheep_net.c - Linux driver for SheepShaver/Basilisk II networking (access to raw Ethernet packets)
3			*
4			* sheep_net (C) 1999 Mar"c" Hellwig and Christian Bauer
5			*
6			* This program is free software; you can redistribute it and/or modify
7			* it under the terms of the GNU General Public License as published by
8			* the Free Software Foundation; either version 2 of the License, or
9			* (at your option) any later version.
10			*
11			* This program is distributed in the hope that it will be useful,
12			* but WITHOUT ANY WARRANTY; without even the implied warranty of
13			* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14			* GNU General Public License for more details.
15			*
16			* You should have received a copy of the GNU General Public License
17			* along with this program; if not, write to the Free Software
18			* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
19			*/
20
21			#include <linux/kernel.h>
22			#include <linux/module.h>
23			#include <linux/version.h>
24			#include <linux/miscdevice.h>
25			#include <linux/netdevice.h>
26			#include <linux/etherdevice.h>
27			#include <linux/if_ether.h>
28			#include <linux/if_arp.h>
29			#include <linux/fs.h>
30			#include <linux/poll.h>
31			#include <linux/init.h>
32			#include <net/sock.h>
33			#include <asm/uaccess.h>
34
35			#define DEBUG 0
36
37			#define bug printk
38			#if DEBUG
39			#define D(x) (x);
40			#else
41			#define D(x) ;
42			#endif
43
44
45			// Constants
46			#define SHEEP_NET_MINOR 198 // Driver minor number
47			#define MAX_QUEUE 32 // Maximum number of packets in queue
48			#define PROT_MAGIC 1520 // Our "magic" protocol type
49
50			// Prototypes
51			static int sheep_net_open(struct inode inode, struct file f);
52			static int sheep_net_release(struct inode inode, struct file f);
53			static ssize_t sheep_net_read(struct file f, char buf, size_t count, loff_t *off);
54			static ssize_t sheep_net_write(struct file f, const char buf, size_t count, loff_t *off);
55			static unsigned int sheep_net_poll(struct file f, struct poll_table_struct wait);
56			static int sheep_net_ioctl(struct inode inode, struct file f, unsigned int code, unsigned long arg);
57			static int sheep_net_receiver(struct sk_buff skb, struct device dev, struct packet_type *pt);
58
59
60			/*
61			* Driver private variables
62			*/
63
64			struct SheepVars {
65			struct device *ether; // The Ethernet device we're attached to
66			struct sock *skt; // Socket for communication with Ethernet card
67			struct sk_buff_head queue; // Receiver packet queue
68			struct packet_type pt; // Receiver packet type
69			struct wait_queue *wait; // Wait queue for blocking read operations
70			};
71
72
73			/*
74			* file_operations structure - has function pointers to the
75			* various entry points for device operations
76			*/
77
78			static struct file_operations sheep_net_fops = {
79			NULL, // llseek
80			sheep_net_read,
81			sheep_net_write,
82			NULL, // readdir
83			sheep_net_poll,
84			sheep_net_ioctl,
85			NULL, // mmap
86			sheep_net_open,
87			NULL, // flush
88			sheep_net_release,
89			NULL, // fsync
90			NULL, // fasync
91			NULL, // check_media_change
92			NULL, // revalidate
93			NULL // lock
94			};
95
96
97			/*
98			* miscdevice structure for driver initialization
99			*/
100
101			static struct miscdevice sheep_net_device = {
102			SHEEP_NET_MINOR, // minor number
103			"sheep_net", // name
104			&sheep_net_fops,
105			NULL,
106			NULL
107			};
108
109
110			/*
111			* Initialize module
112			*/
113
114			int init_module(void)
115			{
116			int ret;
117
118			// Register driver
119			ret = misc_register(&sheep_net_device);
120			D(bug("Sheep net driver installed\n"));
121			return ret;
122			}
123
124
125			/*
126			* Deinitialize module
127			*/
128
129			int cleanup_module(void)
130			{
131			int ret;
132
133			// Unregister driver
134			ret = misc_deregister(&sheep_net_device);
135			D(bug("Sheep net driver removed\n"));
136			return ret;
137			}
138
139
140			/*
141			* Driver open() function
142			*/
143
144			static int sheep_net_open(struct inode inode, struct file f)
145			{
146			struct SheepVars *v;
147			D(bug("sheep_net: open\n"));
148
149			// Must be opened with read permissions
150			if ((f->f_flags & O_ACCMODE) == O_WRONLY)
151			return -EPERM;
152
153			// Allocate private variables
154			v = (struct SheepVars *)f->private_data = kmalloc(sizeof(struct SheepVars), GFP_USER);
155			if (v == NULL)
156			return -ENOMEM;
157			memset(v, 0, sizeof(struct SheepVars));
158			skb_queue_head_init(&v->queue);
159
160			// Yes, we're open
161			MOD_INC_USE_COUNT;
162			return 0;
163			}
164
165
166			/*
167			* Driver release() function
168			*/
169
170			static int sheep_net_release(struct inode inode, struct file f)
171			{
172			struct SheepVars v = (struct SheepVars )f->private_data;
173			struct sk_buff *skb;
174			D(bug("sheep_net: close\n"));
175
176			// Detach from Ethernet card
177			if (v->ether) {
178			dev_remove_pack(&v->pt);
179			sk_free(v->skt);
180			v->skt = NULL;
181			v->ether = NULL;
182			}
183
184			// Empty packet queue
185			while ((skb = skb_dequeue(&v->queue)) != NULL)
186			dev_kfree_skb(skb);
187
188			// Free private variables
189			kfree(v);
190
191			// Sorry, we're closed
192			MOD_DEC_USE_COUNT;
193			return 0;
194			}
195
196
197			/*
198			* Driver read() function
199			*/
200
201			static ssize_t sheep_net_read(struct file f, char buf, size_t count, loff_t *off)
202			{
203			struct SheepVars v = (struct SheepVars )f->private_data;
204			struct sk_buff *skb;
205			sigset_t sigs;
206			int i;
207			D(bug("sheep_net: read\n"));
208
209			for (;;) {
210
211			// Get next packet from queue
212			start_bh_atomic();
213			skb = skb_dequeue(&v->queue);
214			end_bh_atomic();
215			if (skb != NULL \|\| (f->f_flags & O_NONBLOCK))
216			break;
217
218			// No packet in queue and in blocking mode, so block
219			interruptible_sleep_on(&v->wait);
220
221			// Signal received? Then bail out
222			signandsets(&sigs, &current->signal, &current->blocked);
223			for (i=0; i<_NSIG_WORDS; i++) {
224			if (sigs.sig[i])
225			return -EINTR;
226			}
227			}
228			if (skb == NULL)
229			return -EAGAIN;
230
231			// Pass packet to caller
232			if (count > skb->len)
233			count = skb->len;
234			if (copy_to_user(buf, skb->data, count))
235			count = -EFAULT;
236			dev_kfree_skb(skb);
237			return count;
238			}
239
240
241			/*
242			* Driver write() function
243			*/
244
245			static ssize_t sheep_net_write(struct file f, const char buf, size_t count, loff_t *off)
246			{
247			struct SheepVars v = (struct SheepVars )f->private_data;
248			struct sk_buff *skb;
249			char *p;
250			D(bug("sheep_net: write\n"));
251
252			// Check packet size
253			if (count < sizeof(struct ethhdr))
254			return -EINVAL;
255			if (count > 1514)
256			count = 1514;
257
258			// Interface active?
259			if (v->ether == NULL)
260			return count;
261
262			// Allocate buffer for packet
263			skb = dev_alloc_skb(count);
264			if (skb == NULL)
265			return -ENOBUFS;
266
267			// Stuff packet in buffer
268			p = skb_put(skb, count);
269			if (copy_from_user(p, buf, count)) {
270			kfree_skb(skb);
271			return -EFAULT;
272			}
273
274			// Transmit packet
275			dev_lock_list();
276			atomic_add(skb->truesize, &v->skt->wmem_alloc);
277			skb->sk = v->skt;
278			skb->dev = v->ether;
279			skb->priority = 0;
280			skb->protocol = PROT_MAGIC; // "Magic" protocol value to recognize our packets in sheep_net_receiver()
281			skb->nh.raw = skb->h.raw = skb->data + v->ether->hard_header_len;
282			dev_unlock_list();
283			dev_queue_xmit(skb);
284			return count;
285			}
286
287
288			/*
289			* Driver poll() function
290			*/
291
292			static unsigned int sheep_net_poll(struct file f, struct poll_table_struct wait)
293			{
294			struct SheepVars v = (struct SheepVars )f->private_data;
295			D(bug("sheep_net: poll\n"));
296
297			// Packets in queue? Then return
298			start_bh_atomic();
299			if (!skb_queue_empty(&v->queue)) {
300			end_bh_atomic();
301			return POLLIN \| POLLRDNORM;
302			}
303
304			// Otherwise wait for packet
305			poll_wait(f, &v->wait, wait);
306			if (!skb_queue_empty(&v->queue)) {
307			end_bh_atomic();
308			return POLLIN \| POLLRDNORM;
309			} else {
310			end_bh_atomic();
311			return 0;
312			}
313			}
314
315
316			/*
317			* Driver ioctl() function
318			*/
319
320			static int sheep_net_ioctl(struct inode inode, struct file f, unsigned int code, unsigned long arg)
321			{
322			struct SheepVars v = (struct SheepVars )f->private_data;
323			D(bug("sheep_net: ioctl %04x\n", code));
324
325			switch (code) {
326
327			// Attach to Ethernet card
328			// arg: pointer to name of Ethernet device (char[8])
329			case SIOCSIFLINK: {
330			char name[8];
331
332			// Already attached?
333			if (v->ether)
334			return -EBUSY;
335
336			// Get Ethernet card name
337			if (copy_from_user(name, (void *)arg, 8))
338			return -EFAULT;
339			name[7] = 0;
340
341			// Find card
342			dev_lock_list();
343			v->ether = dev_get(name);
344			if (v->ether == NULL) {
345			dev_unlock_list();
346			return -ENODEV;
347			}
348
349			// Is it Ethernet?
350			if (v->ether->type != ARPHRD_ETHER) {
351			v->ether = NULL;
352			dev_unlock_list();
353			return -EINVAL;
354			}
355
356			// Allocate socket
357			v->skt = sk_alloc(0, GFP_USER, 1);
358			if (v->skt == NULL) {
359			v->ether = NULL;
360			dev_unlock_list();
361			return -ENOMEM;
362			}
363			v->skt->dead = 1;
364
365			// Attach packet handler
366			v->pt.type = htons(ETH_P_ALL);
367			v->pt.dev = v->ether;
368			v->pt.func = sheep_net_receiver;
369			v->pt.data = v;
370			dev_add_pack(&v->pt);
371			dev_unlock_list();
372			return 0;
373			}
374
375			// Get hardware address of Ethernet card
376			// arg: pointer to buffer (6 bytes) to store address
377			case SIOCGIFADDR:
378			if (v->ether == NULL)
379			return -ENODEV;
380			if (copy_to_user((void *)arg, v->ether->dev_addr, 6))
381			return -EFAULT;
382			return 0;
383
384			// Add multicast address
385			// arg: pointer to address (6 bytes)
386			case SIOCADDMULTI: {
387			char addr[6];
388			if (v->ether == NULL)
389			return -ENODEV;
390			if (copy_from_user(addr, (void *)arg, 6))
391			return -EFAULT;
392			return dev_mc_add(v->ether, addr, 6, 0);
393			}
394
395			// Remove multicast address
396			// arg: pointer to address (6 bytes)
397			case SIOCDELMULTI: {
398			char addr[6];
399			if (v->ether == NULL)
400			return -ENODEV;
401			if (copy_from_user(addr, (void *)arg, 6))
402			return -EFAULT;
403			return dev_mc_delete(v->ether, addr, 6, 0);
404			}
405
406			// Return size of first packet in queue
407			case FIONREAD: {
408			int count = 0;
409			struct sk_buff *skb;
410			start_bh_atomic();
411			skb = skb_peek(&v->queue);
412			if (skb)
413			count = skb->len;
414			end_bh_atomic();
415			return put_user(count, (int *)arg);
416			}
417
418			default:
419			return -ENOIOCTLCMD;
420			}
421			}
422
423
424			/*
425			* Packet receiver function
426			*/
427
428			static int sheep_net_receiver(struct sk_buff skb, struct device dev, struct packet_type *pt)
429			{
430			struct SheepVars v = (struct SheepVars )pt->data;
431			D(bug("sheep_net: packet received\n"));
432
433			// Packet sent by us? Then discard
434			if (skb->protocol == PROT_MAGIC) {
435			kfree_skb(skb);
436			return 0;
437			}
438
439			// Discard packets if queue gets too full
440			if (skb_queue_len(&v->queue) > MAX_QUEUE) {
441			kfree_skb(skb);
442			return 0;
443			}
444
445			// We also want the Ethernet header
446			skb_push(skb, skb->data - skb->mac.raw);
447
448			// Enqueue packet
449			start_bh_atomic();
450			skb_queue_tail(&v->queue, skb);
451			end_bh_atomic();
452
453			// Unblock blocked read
454			wake_up(&v->wait);
455			return 0;
456			}