Hi, whereas COMMAND_LINE_SIZE is used inside the Linux kernel and can be adjusted there (it already has different values for different plat- forms), Xen uses another constant, MAX_CMDLINE, at different places where start preparations are done. Unfortunately, MAX_CMDLINE is set to a fixed 256 in xen/include/public/xen.h without consulting which value is possible for dom0 kernels (linux/include/asm-xen/asm-i386/setup.h) which can then lead to a cmd line cut-off. Is there special reason why this is the case? Regards, -- Birger Tödtmann Technik der Rechnernetze, Institut für Experimentelle Mathematik Universität Duisburg-Essen, Campus Essen email:btoedtmann@iem.uni-due.de skype:birger.toedtmann pgp:0x6FB166C9 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
> whereas COMMAND_LINE_SIZE is used inside the Linux kernel and > can be adjusted there (it already has different values for > different plat- forms), Xen uses another constant, > MAX_CMDLINE, at different places where start preparations are > done. Unfortunately, MAX_CMDLINE is set to a fixed 256 in > xen/include/public/xen.h without consulting which value is > possible for dom0 kernels (linux/include/asm-xen/asm-i386/setup.h) > which can then lead to a cmd line cut-off. Is there special > reason why > this is the case?MAX_CMDLINE is used in the definition of start_info_t, which is the structure used to pass information into guests when they are created. It''s part of the public hypervisor interface, so you wouldn''t want it dependent on the particular dom0 kernel. However, it''s the last item in the structure, which means we could increase it without breaking backward compatibility. I can see some justification to doing this as I''ve run in to trouble before with iscsi root command lines. Do any of the distro kernels increase COMMAND_LINE_SIZE beyond 256? Ian _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Am Mittwoch, den 08.06.2005, 07:58 +0100 schrieb Ian Pratt: [...]> > MAX_CMDLINE is used in the definition of start_info_t, which is the structure used to pass information into guests when they are created. It''s part of the public hypervisor interface, so you wouldn''t want it dependent on the particular dom0 kernel. However, it''s the last item in the structure, which means we could increase it without breaking backward compatibility. > > I can see some justification to doing this as I''ve run in to trouble before with iscsi root command lines. Do any of the distro kernels increase COMMAND_LINE_SIZE beyond 256?My point is that you cannot predict which guests you are going to run and what cmd line sizes they may offer. Currently i386 cmd line sizes are at 256, but I don''t know about Net/FreeBSD, and a ''grep COMMAND_LINE_SIZE'' on the linux kernel suggests quite a variety of lengths up to 1024 (arm architecture). I myself frequently increase them to support different configuration hints for the guests, I think that''s also a reason why the size for UML currently is at 512. So fixing MAX_CMDLINE at 256 looks a bit .... arbitrary? I had quite some difficulties even to find out that *Xen* is cutting off my args, not the kernel I am booting ;-) Regards, -- Birger Tödtmann Technik der Rechnernetze, Institut für Experimentelle Mathematik Universität Duisburg-Essen, Campus Essen email:btoedtmann@iem.uni-due.de skype:birger.toedtmann pgp:0x6FB166C9 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel