fatal: git grep: cannot generate relative filenames containing '..'

["George Spelvin" <linux@horizon.com>]

Could someone fix this some day?  "git grep <pattern> ../include"
is something I find myself wanting quite frequently, and it's a fresh
annoyance every time I type it to discover that it still doesn't work.

While you're at it, an option to search the entire git tree rather than
the current subdirectory would also be useful.  I was thinking about
a flag like -r (for "root"), but a second idea dawned on me: interpret
absolute pathnames as relative to the root of the repository.  So I could
"git grep <pattern> /" or "git grep <pattern> /include" from any subdirectory.

As it is currently, absolute pathnames don't work very well either...
[1]$ git grep xyzzy $PWD
fatal: '/home/linux/project/src' is outside repository
[2]$ cd /usr/src/linux
[3]$ git grep xyzzy $PWD
CREDITS:E: rjd@xyzzy.clara.co.uk
drivers/hwmon/hwmon-vid.c: * With assistance from Trent Piepho <xyzzy@speakeasy.
drivers/infiniband/hw/ipath/ipath_debug.h: * if(infinipath_debug & _IPATH_xyzzy)
drivers/media/dvb/frontends/or51132.c: *    Copyright (C) 2007 Trent Piepho <xyz
drivers/media/video/cx88/cx88-alsa.c: *    (c) 2007 Trent Piepho <xyzzy@speakeas
drivers/video/intelfb/intelfbhw.c:      /* do some funky magic - xyzzy */
include/linux/byteorder/swab.h: * Trent Piepho <xyzzy@speakeasy.org> 2007114
include/linux/hwmon-vid.h:    With assistance from Trent Piepho <xyzzy@speakeasy
[4]$ cd include
[5]$ git grep xyzzy $PWD
fatal: git grep: cannot generate relative filenames containing '..'

I don't quite understand that last error message.

Thank you.