Messages in this thread | | | Date | Wed, 31 Aug 2005 14:29:44 -0700 | From | "H. Peter Anvin" <> | Subject | Re: THE LINUX/I386 BOOT PROTOCOL - Breaking the 256 limit |
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Alon Bar-Lev wrote: > > Hello Peter, > > I am sorry that I am contacting you directly... Please refer me to > correct contact if you are not the one. > > Lately, I've found that 256 bytes long kernel parameters are not enough > for my configuration. > > I've found the place where the kernel defines the length, I've actually > found it in two places... I cannot understand why... > > include/asm-i386/param.h: #define COMMAND_LINE_SIZE 256 > include/asm-i386/setup.h: #define COMMAND_LINE_SIZE 256 > > Now... I've added an entry in the kernel configuration menu so that I > can define these constants using menuconfig. > > I was quite happy... > > But then I've got into a discussion with grub's development team... > > From what I've read in the Documentation/i386/boot.txt I understood > that if I use boot protocol 2.02+ there should be no reason for 256 byte > limitation on the string pointed by the cmd_line_ptr, so I guessed they > will deliver the command-line twice once for the old protocol truncated, > and once for the new protocol not truncated. > > Grub and Lilo approach is to point the cmd_line_ptr to the old > protocol's command line, thus truncating it to 256. > > I'm just wondering... Can the 256 limit be broken, without modifying the > boot protocol? > > I think it can... But I need a formal answer so I can push it forward. >
Yes, it can. Several people on the SYSLINUX mailing list have tried this, and it works just fine. The current version of SYSLINUX has a limit of 511 characters (because of memory management reasons inside SYSLINUX) instead of 255 (plus null).
I think someone on the SYSLINUX mailing list already sent a patch to akpm to make 512 the default; making it configurable would be a better idea. Feel free to send your patch through me.
-hpa
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