Re: [PATCH] pac_common: redesign function for finding Start Of Frame

From: NÃmeth MÃrton
Date: Sun Oct 04 2009 - 16:58:20 EST

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Hi,

I wrote a simple test for pac_find_sof(). I implemented a user-space test
which takes the implementation from the source file and calls it directly.
You can find the source code of the test attached.

The test results for the pac_find_sof() implementation in the Linux kernel
2.6.32-rc1 is the following:

Test case 1: exact match
PDEBUG: SOF found, bytes to analyze: 5. Frame starts at byte #5
PASSED

Test case 2: offset 1
PDEBUG: SOF found, bytes to analyze: 6. Frame starts at byte #6
PASSED

Test case 3: offset 1, first byte may be misleading
FAILED

Test case 4: offset 2, first two bytes may be misleading
PDEBUG: SOF found, bytes to analyze: 7. Frame starts at byte #7
PASSED

Test case 5: offset 3, first three bytes may be misleading
FAILED

Test case 6: offset 4, first four bytes may be misleading
FAILED

Test case 7: pattern starts at end of packet and continues in the next one
PDEBUG: SOF found, bytes to analyze: 1. Frame starts at byte #1
PASSED

Test case 8: splited pattern, with misleading first byte
FAILED

Test case 9: splited pattern, with misleading first three bytes
FAILED

Test case 10: no match, extra byte at offset 1
PASSED

Test case 11: no match, extra byte at offset 2
PASSED

Test case 12: no match, extra byte at offset 3
PASSED

Test case 13: no match, extra byte at offset 4
PASSED

I also executed the test with the patched pac_find_sof() implementation
and that one passes all these test cases.

Regards,

MÃrton NÃmeth

NÃmeth MÃrton wrote:
> From: MÃrton NÃmeth <nm127@xxxxxxxxxxx>
>
> The original implementation of pac_find_sof() does not always find
> the Start Of Frame (SOF) marker. Replace it with a state machine
> based design.
>
> The change was tested with Labtec Webcam 2200.
>
> Signed-off-by: MÃrton NÃmeth <nm127@xxxxxxxxxxx>
> ---
> --- linux-2.6.32-rc1.orig/drivers/media/video/gspca/pac_common.h 2009-09-10 00:13:59.000000000 +0200
> +++ linux-2.6.32-rc1/drivers/media/video/gspca/pac_common.h 2009-10-04 21:49:19.000000000 +0200
> @@ -33,6 +33,45 @@
> static const unsigned char pac_sof_marker[5] =
> { 0xff, 0xff, 0x00, 0xff, 0x96 };
>
> +/*
> + The following state machine finds the SOF marker sequence
> + 0xff, 0xff, 0x00, 0xff, 0x96 in a byte stream.
> +
> + +----------+
> + | 0: START |<---------------\
> + +----------+<-\ |
> + | \---/otherwise |
> + v 0xff |
> + +----------+ otherwise |
> + | 1 |--------------->*
> + | | ^
> + +----------+ |
> + | |
> + v 0xff |
> + +----------+<-\0xff |
> + /->| |--/ |
> + | | 2 |--------------->*
> + | | | otherwise ^
> + | +----------+ |
> + | | |
> + | v 0x00 |
> + | +----------+ |
> + | | 3 | |
> + | | |--------------->*
> + | +----------+ otherwise ^
> + | | |
> + 0xff | v 0xff |
> + | +----------+ |
> + \--| 4 | |
> + | |----------------/
> + +----------+ otherwise
> + |
> + v 0x96
> + +----------+
> + | FOUND |
> + +----------+
> +*/
> +
> static unsigned char *pac_find_sof(struct gspca_dev *gspca_dev,
> unsigned char *m, int len)
> {
> @@ -41,17 +80,54 @@ static unsigned char *pac_find_sof(struc
>
> /* Search for the SOF marker (fixed part) in the header */
> for (i = 0; i < len; i++) {
> - if (m[i] == pac_sof_marker[sd->sof_read]) {
> - sd->sof_read++;
> - if (sd->sof_read == sizeof(pac_sof_marker)) {
> + switch (sd->sof_read) {
> + case 0:
> + if (m[i] == 0xff)
> + sd->sof_read = 1;
> + break;
> + case 1:
> + if (m[i] == 0xff)
> + sd->sof_read = 2;
> + else
> + sd->sof_read = 0;
> + break;
> + case 2:
> + switch (m[i]) {
> + case 0x00:
> + sd->sof_read = 3;
> + break;
> + case 0xff:
> + /* stay in this state */
> + break;
> + default:
> + sd->sof_read = 0;
> + }
> + break;
> + case 3:
> + if (m[i] == 0xff)
> + sd->sof_read = 4;
> + else
> + sd->sof_read = 0;
> + break;
> + case 4:
> + switch (m[i]) {
> + case 0x96:
> + /* Pattern found */
> PDEBUG(D_FRAM,
> "SOF found, bytes to analyze: %u."
> " Frame starts at byte #%u",
> len, i + 1);
> sd->sof_read = 0;
> return m + i + 1;
> + break;
> + case 0xff:
> + sd->sof_read = 2;
> + break;
> + default:
> + sd->sof_read = 0;
> }
> - } else {
> + break;
> + default:
> sd->sof_read = 0;
> }
> }
>

/*
Test the function pac_find_sof() from file
linux/drivers/media/video/gspca/pac_common.h

Test based on Linux kernel 2.6.32-rc1
Written by MÃ¡rton NÃ©meth <nm127@xxxxxxxxxxx>, 4 Oct 2009
Released under GPL
*/

#include <stdio.h>

struct sd {
unsigned int sof_read;
};

struct gspca_dev {
struct sd* sd;
};

#define PDEBUG(level, fmt, args...) \
do {\
printf("PDEBUG: " fmt "\n", ## args); \
} while (0)

#include "pac_common.h"

int tc1() {
static unsigned char test[] = { 0xff, 0xff, 0x00, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 1: exact match\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == &test[5]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc2() {
static unsigned char test[] = { 0x00, 0xff, 0xff, 0x00, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 2: offset 1\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == &test[6]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc3() {
static unsigned char test[] = { 0xff, 0xff, 0xff, 0x00, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 3: offset 1, first byte may be misleading\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == &test[6]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc4() {
static unsigned char test[] = { 0xff, 0x00, 0xff, 0xff, 0x00, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 4: offset 2, first two bytes may be misleading\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == &test[7]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc5() {
static unsigned char test[] = { 0xff, 0xff, 0x00, 0xff, 0xff, 0x00, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 5: offset 3, first three bytes may be misleading\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == &test[8]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc6() {
static unsigned char test[] = { 0xff, 0xff, 0x00, 0xff, 0xff, 0xff, 0x00, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 6: offset 4, first four bytes may be misleading\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == &test[9]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc7() {
static unsigned char test1[] = { 0xff, 0xff, 0x00, 0xff };
static unsigned char test2[] = { 0x96 };
unsigned char* p1;
unsigned char* p2;
struct sd sd;
int result = 0;

printf("Test case 7: pattern starts at end of packet and continues in the next one\n");
sd.sof_read = 0;
p1 = pac_find_sof((struct gspca_dev*)&sd, test1, sizeof(test1));
p2 = pac_find_sof((struct gspca_dev*)&sd, test2, sizeof(test2));
if (p1 == NULL && p2 == &test2[1]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc8() {
static unsigned char test1[] = { 0xff, 0xff, 0xff, 0x00, 0xff };
static unsigned char test2[] = { 0x96 };
unsigned char* p1;
unsigned char* p2;
struct sd sd;
int result = 0;

printf("Test case 8: splited pattern, with misleading first byte\n");
sd.sof_read = 0;
p1 = pac_find_sof((struct gspca_dev*)&sd, test1, sizeof(test1));
p2 = pac_find_sof((struct gspca_dev*)&sd, test2, sizeof(test2));
if (p1 == NULL && p2 == &test2[1]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc9() {
static unsigned char test1[] = { 0xff, 0xff, 0x00, 0xff, 0xff, 0x00, 0xff };
static unsigned char test2[] = { 0x96 };
unsigned char* p1;
unsigned char* p2;
struct sd sd;
int result = 0;

printf("Test case 9: splited pattern, with misleading first three bytes\n");
sd.sof_read = 0;
p1 = pac_find_sof((struct gspca_dev*)&sd, test1, sizeof(test1));
p2 = pac_find_sof((struct gspca_dev*)&sd, test2, sizeof(test2));
if (p1 == NULL && p2 == &test2[1]) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc10() {
static unsigned char test[] = { 0xff, 0xaa, 0xff, 0x00, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 10: no match, extra byte at offset 1\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == NULL) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc11() {
static unsigned char test[] = { 0xff, 0xff, 0xaa, 0x00, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 11: no match, extra byte at offset 2\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == NULL) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc12() {
static unsigned char test[] = { 0xff, 0xff, 0x00, 0xaa, 0xff, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 12: no match, extra byte at offset 3\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == NULL) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int tc13() {
static unsigned char test[] = { 0xff, 0xff, 0x00, 0xff, 0xaa, 0x96 };
unsigned char* p;
struct sd sd;
int result = 0;

printf("Test case 13: no match, extra byte at offset 4\n");
sd.sof_read = 0;
p = pac_find_sof((struct gspca_dev*)&sd, test, sizeof(test));
if (p == NULL) {
printf("PASSED\n");
} else {
printf("FAILED\n");
result = 1;
}
printf("\n");

return result;
}

int main() {
int result = 0;

result += tc1();
result += tc2();
result += tc3();
result += tc4();
result += tc5();
result += tc6();
result += tc7();
result += tc8();
result += tc9();
result += tc10();
result += tc11();
result += tc12();
result += tc13();

return result;
}

Next message: Jiri Kosina: "Re: [PATCH] spelling correction in a comment"
Previous message: NÃmeth MÃrton: "[PATCH] pac_common: redesign function for finding Start Of Frame"
In reply to: NÃmeth MÃrton: "[PATCH] pac_common: redesign function for finding Start Of Frame"
Next in thread: Hans de Goede: "Re: [PATCH] pac_common: redesign function for finding Start Of Frame"
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