Rob, On Thu, Nov 27, 2008 at 8:35 AM, Rob Landley <rob@xxxxxxxxxxx> wrote: > http://kernel.org/doc/man-pages/online/pages/man2/uname.2.html > > It says the length of the fields was unspecified. Yup -- that's what POSIX says. > Initially I thought that > meant it was implemented as each field starting right after the previous one's > null terminator, (Not sure why you would assume that.) > but it turns out that each field is exactly 65 characters > long. Well, yes. That info is lower down in the page: Over time, increases in the size of the utsname structure have led to three successive versions of uname(): sys_olduname() (slot __NR_oldolduname), sys_uname() (slot __NR_olduname), and sys_newuname() (slot __NR_uname). The first one used length 9 for all fields; the second used 65; the third also uses 65 but adds the domainname field. The glibc uname() wrapper function hides these details from applications, invoking the most recent version of the system call provided by the kernel. > This is hardwired into both bits/utsname.h and linux/utsname.h, and more to > the point you can't talk to the kernel without knowing what this value _is_, Why do you claim this? As noted in the first para of the description, the fields of the structure are null-terminated, which, in the typical case, makes it quite possible to use them without knowing their (maximum) lengths. And indeed, a portable program should not care. > so leaving it unspecified is silly. It's part of the current kernel's binary > abi, and the value is currently 65. And that last piece is exactly part of the problem, because once upon a time (okay: a long time ago, now), it was true that "the value is currently 9". It seems to me that all the info you needed was there in the page, but you didn't read the whole page. The question is, whether the page could/should provide more clues to make sure that the reader is pointed to the fine details (which, for the reasons I described above, are often not needed). Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
