ulimit: raise default hard ulimit on number of files to 4096

Apps are increasingly using more than 1024 file descriptors.  See
discussion in several distro bug trackers, e.g.  BugLink:
http://bugs.launchpad.net/bugs/663090
https://issues.rpath.com/browse/RPL-2054

You don't want to raise the default soft limit, since that might break
apps that use select(), but it's safe to raise the default hard limit;
that way, apps that know they need lots of file descriptors can raise
their soft limit without needing root, and without user intervention.

Ubuntu is doing this with a kernel change because they have a policy of
not changing kernel defaults in userland.

While 4096 might not be enough for *all* apps, it seems to be plenty for
the apps I've seen lately that are unhappy with 1024.
Signed-off-by: NTim Gardner <tim.gardner@canonical.com>
Cc: Dan Kegel <dank@kegel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/asm-generic/resource.h

@@ -78,7 +78,7 @@
 	[RLIMIT_CORE]		= {              0,  RLIM_INFINITY },	\
 	[RLIMIT_RSS]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\
 	[RLIMIT_NPROC]		= {              0,              0 },	\
-	[RLIMIT_NOFILE]		= {       INR_OPEN,       INR_OPEN },	\
+	[RLIMIT_NOFILE]		= {   INR_OPEN_CUR,   INR_OPEN_MAX },	\
 	[RLIMIT_MEMLOCK]	= {    MLOCK_LIMIT,    MLOCK_LIMIT },	\
 	[RLIMIT_AS]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\
 	[RLIMIT_LOCKS]		= {  RLIM_INFINITY,  RLIM_INFINITY },	\

include/linux/fs.h

@@ -23,7 +23,8 @@
 
 /* Fixed constants first: */
 #undef NR_OPEN
-#define INR_OPEN 1024		/* Initial setting for nfile rlimits */
+#define INR_OPEN_CUR 1024	/* Initial setting for nfile rlimits */
+#define INR_OPEN_MAX 4096	/* Hard limit for nfile rlimits */
 
 #define BLOCK_SIZE_BITS 10
 #define BLOCK_SIZE (1<<BLOCK_SIZE_BITS)