On Friday 07 May 2004 03:32, Danilo Reinhardt wrote:
> Thanks Jim!
>
> I think about your suggested code, and maybe i dont understand what
> your variables stand for, or .... ok, i think i dont understand ;)
>
> Thats the lines i dont understand.
>
> pos = begin + len; // pos is file offset of last byte in buffer
> if (pos < off) {
> len = 0; // We havn't hit offset yet, start over
> begin = pos;
> }
>
> How do you calc begin? begin = page+off ?
'begin' is initialized to 0. begin and pos are both offsets.
> If so, the if statement would never been true. Because, offset it's
> small , in my case up to 1024, and pos is a memory address, really
> big... do you has the complete function source?
Variables names are different, but this is a generic version
of what I have. The my_lock isn't needed for this example, but
I just left it in because some sort of locking will likely be needed
in any real code. The POS_CHECK macro comes in handy if you
have multiple loops.
static rwlock_t my_lock = RW_LOCK_UNLOCKED;
/*
* handler for a /proc file that
* prints out 1000 lines of "foo bar"
*
* Note: 'buffer' is one page long and 'length' will
* never be more then 3KiB.
*/
int my_read_proc(char *buffer, char **start, off_t offset,
int length, int *eof, void *data) {
off_t pos = 0;
off_t begin = 0;
int len = 0;
int i;
#define POS_CHECK() do { \
pos = begin + len; \
if (pos < offset) { \
len = 0; \
begin = pos; \
} \
if (pos > offset + length) \
goto done; \
} while (0)
read_lock(&my_lock);
for (i=0; i<1000; i++) {
len += sprintf(buffer+len, "foo ");
len += sprintf(buffer+len, "bar\n");
POS_CHECK();
}
*eof = 1;
done:
read_unlock(&my_lock);
*start = buffer + (offset - begin);
len -= (offset - begin);
if (len > length)
len = length;
if (len < 0)
len = 0;
return len;
}
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