With the kernel module *samples/kfifo/inttype-example.ko*, the system will
create file /proc/int-fifo.
but the current code for this module may have some bug, as the following:
# echo 100 > /proc/int-fifo ----------------> OK
# echo 1000000 > /proc/int-fifo ----------------> OK
# echo 99 > /proc/int-fifo ----------------> Never return
# echo 1000 > /proc/int-fifo ----------------> Never return
so i found that, the length of the content putting into /proc/int-fifo must be
4, 8, 12 .....
another idea:
this kernel module is about a FIFO which type is int. we should put an interger
into it, not the string.
when we reading from this file, we should get all elements in the FIFO. just as
the following:
# echo 1 > /proc/int-fifo
# echo 2 > /proc/int-fifo
# echo 3 > /proc/int-fifo
# cat /proc/int-fifo
1
2
3
# echo 101 > /proc/int-fifo
# echo 103 > /proc/int-fifo
# echo 104 > /proc/int-fifo
# echo 102 > /proc/int-fifo
# cat /proc/int-fifo
101
103
104
102
with my patch, we can echo an integer into the FIFO. so the following command
is OK.
echo 1 > /proc/int-fifo
without my patch, the command `echo 1 > /proc/int-fifo` will never return,
beacuse the following code:
223 int __kfifo_from_user(struct __kfifo *fifo, const void __user *from,
224 unsigned long len, unsigned int *copied)
225 {
226 unsigned int l;
227 unsigned long ret;
228 unsigned int esize = fifo->esize;
229 int err;
230
231 if (esize != 1)
232 len /= esize;
233
234 l = kfifo_unused(fifo);
235 if (len > l)
236 len = l;
237
238 ret = kfifo_copy_from_user(fifo, from, len, fifo->in, copied);
239 if (unlikely(ret)) {
240 len -= ret;
241 err = -EFAULT;
242 } else
243 err = 0;
244 fifo->in += len;
245 return err;
246 }
247 EXPORT_SYMBOL(__kfifo_from_user);
int the line 231: if len = 3, esize = 4, then at the line 232 len = 0.
Wang Long (1):
samples: Fix `echo 1 > /proc/int-fifo` never return error
samples/kfifo/inttype-example.c | 51 ++++++++++++++++++++++++++++++++---------
1 file changed, 40 insertions(+), 11 deletions(-)
--
1.8.3.1
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