On 09/09/2014 08:51 AM, Eric W. Biederman wrote: > "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> writes: > >> On 08/30/2014 02:53 PM, Eric W. Biederman wrote: >>> "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> writes: >> [...] >> >> >>>> The initial user namespace has no parent namespace, but, for con‐ >>>> sistency, the kernel provides dummy user and group ID mapping >>>> files for this namespace. Looking at the uid_map file (gid_map >>>> is the same) from a shell in the initial namespace shows: >>>> >>>> $ cat /proc/$$/uid_map >>>> 0 0 4294967295 >>>> >>>> This mapping tells us that the range starting at user ID 0 in >>>> this namespace maps to a range starting at 0 in the (nonexistent) >>>> parent namespace, and the length of the range is the largest >>>> 32-bit unsigned integer. >>> >>> Which deliberately leaves 4294967295 32bit (-1) unmapped. (uid_t)-1 is >>> used in several interfaces (like setreuid) as a way to specify no uid >>> leaving it unmapped and unusuable guarantees that there will be no >>> confusion when using those kernel methods. >> >> So, I worked that piece into the text to give: >> >> This mapping tells us that the range starting at user ID 0 in >> this namespace maps to a range starting at 0 in the (nonexis‐ >> tent) parent namespace, and the length of the range is the >> largest 32-bit unsigned integer. (This deliberately leaves >> 4294967295 (the 32-bit signed -1 value) unmapped. This is >> deliberate: (uid_t) -1 is used in several interfaces (e.g., >> setreuid(2)) as a way to specify "no user ID". Leaving >> setreuid(2)) unmapped and unusuable guarantees that there will > ^^^^ (uid_t) -1 (not setreuid(2) >> be no confusion when using these interfaces. >> >> Okay? > > Other than the typo fix above this looks good. Ahhh -- thanks for catching that, Eric. Fixed now. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
