Paolo
===================================================================
RCS file: /tcpdump/master/libpcap/pcap-usb-linux.c,v
retrieving revision 1.20
diff -r1.20 pcap-usb-linux.c
652c652
< usb_read_linux_mmap(pcap_t *handle, int max_packets, pcap_handler
callback, u_char *user)
---
usb_read_linux_mmap(pcap_t *handle, int max_packets, pcap_handler
callback, u_char *user, u_char *buf, u_short bufsize)
696c696
< hdr = (pcap_usb_header*) &handle->buffer[vec[i]];
---
hdr = (pcap_usb_header*) &buf[vec[i]];
Thanks for the fix
Here handle->buffer refers to a memory mapped kernel buffer, which
holds
the USB Request Blocks and related meta-data. To make the patch work
is
necessary to perform a memcpy from the kernel buffer to the user
provided one, but this solution will remove the performance gain of
the
memory mapped access.
perhaps a spinlock will be enough?
In general the question is pretty simple. We have multicore CPUs and
in order to exploit them we need to use threads. Putting a mutex
around pcap is not a good idea as this has a major impact on
performance because the lock around a pcap_xx call is too coarse-
grained. The solution is to make libpcap reentrant either removing
shared data-structures or adding mutexes (better spinlocks) into the
library. As the library is mostly reentrant, I see a value of doing
this effort into libpcap.
Regards, Luca
ciao,
Paolo
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