Fix core dumps of guests > 2 GB in size on i386

["Daniel P. Berrange" <berrange@redhat.com>]

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During testing of Xen 3.0.3 tree we discovered that core dumps of guests
with more than 2 GB of RAM would fail on i386 platforms. A quick look at
the libxc code for generating core files shows that it does not use the
O_LARGEFILE flag or explicit open64 function when opening the file. Thus
the file is limited to 2^31-1 bytes.

The attached patch adds the O_LARGEFILE flag when opening the file. It
is also neccessary to add additional CFLAGS & LDFLAGS to enable use of
the POSIX Largefile  standard.  There are two ways to enable LFS support,
in implicit mode all types, functions & macros are automatically changed
to the 64 bit variants at compile time - this however changes the ABI
contract - eg size_t is now 64-bits instead of 32. The alternate is the
explicit mode, which merely makes 64-bit variants of the calls available
and thus preserves ABI. Thus in this patch I use the explicit LFS mode
and then pass O_LARGEFILE to the open() call flags.

Without this patch you see:

  # xm list
  xm Name                                      ID Mem(MiB) VCPUs State   Time(s)
  Domain-0                                   0     1485     4 r-----   4905.3
  coretest                                   9     2556     1 -b----     15.0
  # xm dump-core coretest
  Dumping core of domain: coretest ...
  Error: Failed to dump core: (27, 'File too large')
  Usage: xm dump-core [-L|--live] [-C|--crash] <Domain> [Filename]
  # ls -l /var/xen/dump/
  total 4721672
  -rw------- 1 root root 2147483647 Nov 15 16:33 2006-1115-1632.46-coretest.9.core-incomplete


With this patch applied:

  # xm list
  Name                                      ID Mem(MiB) VCPUs State   Time(s)
  Domain-0                                   0     1485     4 r-----     29.6
  coretest                                   1     2556     1 r-----      3.1
  # xm dump-core coretest
  Dumping core of domain: coretest ...
  # ls -l /var/xen/dump/
  total 4721672
  -rw------- 1 root root 2682781696 Nov 15 16:58 2006-1115-1657.33-coretest.1.core



  Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

Regards,
Dan.
-- 
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[-- Attachment #2: xen-core-2gb.patch --]
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diff -rc xen-3.0.3_0-src/tools/libxc/Makefile xen-3.0.3_0-src.new/tools/libxc/Makefile
*** xen-3.0.3_0-src/tools/libxc/Makefile	2006-10-15 08:22:03.000000000 -0400
--- xen-3.0.3_0-src.new/tools/libxc/Makefile	2006-11-15 16:08:47.000000000 -0500
***************
*** 39,44 ****
--- 39,48 ----
  CFLAGS   += -fno-strict-aliasing
  CFLAGS   += $(INCLUDES) -I.
  
+ # Enable large file support.
+ CFLAGS   += $(shell getconf LFS64_CFLAGS)
+ LDFLAGS  += $(shell getconf LFS64_LDFLAGS) $(shell getconf LFS64_LIBS)
+ 
  # Define this to make it possible to run valgrind on code linked with these
  # libraries.
  #CFLAGS   += -DVALGRIND -O0 -ggdb3
diff -rc xen-3.0.3_0-src/tools/libxc/xc_core.c xen-3.0.3_0-src.new/tools/libxc/xc_core.c
*** xen-3.0.3_0-src/tools/libxc/xc_core.c	2006-10-15 08:22:03.000000000 -0400
--- xen-3.0.3_0-src.new/tools/libxc/xc_core.c	2006-11-15 16:07:02.000000000 -0500
***************
*** 1,6 ****
--- 1,7 ----
  #include "xg_private.h"
  #include <stdlib.h>
  #include <unistd.h>
+ #include <fcntl.h>
  
  /* number of pages to write at a time */
  #define DUMP_INCREMENT (4 * 1024)
***************
*** 156,162 ****
      struct dump_args da;
      int sts;
  
!     if ( (da.fd = open(corename, O_CREAT|O_RDWR, S_IWUSR|S_IRUSR)) < 0 )
      {
          PERROR("Could not open corefile %s: %s", corename, strerror(errno));
          return -errno;
--- 157,163 ----
      struct dump_args da;
      int sts;
  
!     if ( (da.fd = open(corename, O_CREAT|O_RDWR|O_LARGEFILE, S_IWUSR|S_IRUSR)) < 0 )
      {
          PERROR("Could not open corefile %s: %s", corename, strerror(errno));
          return -errno;

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