Daniel P. Berrange
2006-Nov-15 22:02 UTC
[Xen-devel] Fix core dumps of guests > 2 GB in size on i386
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. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=| _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2006-Nov-17 09:52 UTC
Re: [Xen-devel] Fix core dumps of guests > 2 GB in size on i386
On 15/11/06 22:02, "Daniel P. Berrange" <berrange@redhat.com> wrote:> 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.I like the implicit method. I think it''s unlikely to bite us. A lot of tools subdirs are defining _FILE_OFFSET_BITS=64 anyway (and not using getconf!). I''ll provide a portable common CFLAGS/LDFLAGS addition in tools/Rules.mk. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Daniel P. Berrange
2006-Nov-17 12:12 UTC
Re: [Xen-devel] Fix core dumps of guests > 2 GB in size on i386
On Fri, Nov 17, 2006 at 09:52:15AM +0000, Keir Fraser wrote:> On 15/11/06 22:02, "Daniel P. Berrange" <berrange@redhat.com> wrote: > > > 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. > > I like the implicit method. I think it''s unlikely to bite us. A lot of tools > subdirs are defining _FILE_OFFSET_BITS=64 anyway (and not using getconf!). > I''ll provide a portable common CFLAGS/LDFLAGS addition in tools/Rules.mk.Well there are two methods in libxc which expose a size_t argument so the implicit method will break ABI changing these from 32 to 64 bits. xenctrl.h:int xc_tbuf_enable(int xc_handle, size_t cnt, unsigned long *mfn, xenctrl.h:int xc_acm_op(int xc_handle, int cmd, void *arg, size_t arg_size); They are probably only called from other apps / libraries in the tools/ dir, so perhaps we don''t care about ABI breakage in these two functions. Must make sure the python binding is still working correctly though because a 64-bit size_t on 32-bit arch will no longer fit in Python''s native Int type - will have to switch to Long Regards, Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=| _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2006-Nov-17 13:47 UTC
Re: [Xen-devel] Fix core dumps of guests > 2 GB in size on i386
On 17/11/06 12:12, "Daniel P. Berrange" <berrange@redhat.com> wrote:> Well there are two methods in libxc which expose a size_t argument so the > implicit method will break ABI changing these from 32 to 64 bits. > > xenctrl.h:int xc_tbuf_enable(int xc_handle, size_t cnt, unsigned long *mfn, > xenctrl.h:int xc_acm_op(int xc_handle, int cmd, void *arg, size_t arg_size);It''d be better probably to replace with explicit types and avoid off_t/size_t confusion at all. Maybe uint64_t. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Daniel P. Berrange
2006-Nov-17 18:47 UTC
Re: [Xen-devel] Fix core dumps of guests > 2 GB in size on i386
On Fri, Nov 17, 2006 at 01:47:12PM +0000, Keir Fraser wrote:> On 17/11/06 12:12, "Daniel P. Berrange" <berrange@redhat.com> wrote: > > > Well there are two methods in libxc which expose a size_t argument so the > > implicit method will break ABI changing these from 32 to 64 bits. > > > > xenctrl.h:int xc_tbuf_enable(int xc_handle, size_t cnt, unsigned long *mfn, > > xenctrl.h:int xc_acm_op(int xc_handle, int cmd, void *arg, size_t arg_size); > > It''d be better probably to replace with explicit types and avoid > off_t/size_t confusion at all. Maybe uint64_t.Looking more closely at the python code, it appears the size_t parameters do not get directly exposed to the python, so there should be no data type size issues here to worry about - the size_t param is merely used in the raw C code doing sizeof() on one of the other params. So the patch you''ve already committed to put LFS flags in the top level makefile looks like it''ll be sufficient. Regards, Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=| _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel