Increased limits to allow for large system runs

Increased limits to allow for large system runs

On 16-way w/ 104 disks and a 32-way w/ 96 disks, I was getting:

$ sudo blktrace -b 1024 -n 8 -I ../files
./cciss_c1d6.blktrace.10: Too many open files
Failed to start worker threads

Due to the nature of our N(cpus) X N(devices) order of file opens, and
our N(cpus) X N(devices) X N(buffers) X (buffer size) amount of mmaps()
going on we're exceeding both the RLIMIT_NOFILE and RLIMIT_MEMLOCK
limits.

This patch raises limits for RLIMIT_NOFILE and RLIMIT_MEMLOCK to
"infinity", and allows blktrace to handle the large(ish) systems. (If
these settings fail, we "guestimate" about how much we really need.)

There is still an underlying blktrace and/or kernel problem: The
directory /sys/kernel/debug/block/<DSF> where <DSF> is the device that
encountered the limit is left behind (not cleaned up correctly). This
stops blktrace from running a second time (even on another device):

$  ls /sys/kernel/debug/block
cciss_c1d6
$ sudo blktrace /dev/sda
BLKTRACESETUP: No such file or directory
Failed to start trace on /dev/sda

and requires a reboot. (Looking into that next, as this patch - whilst
stopping the original problem from happening - does not address the
secondary problem. And there may be some other ways for the secondary
problem to still occur...)

I also fixed a warning concerning ftruncate's return value being
ignored.

Signed-off-by: Alan D. Brunelle <alan.brunelle@hp.com>
Signed-off-by: Jens Axboe <axboe@carl.(none)>