On 2020-03-30, Michael Kerrisk (man-pages) wrote: > Hello Aleksa, > > On 2/2/20 4:19 PM, Aleksa Sarai wrote: > > Rather than trying to merge the new syscall documentation into open.2 > > (which would probably result in the man-page being incomprehensible), > > instead the new syscall gets its own dedicated page with links between > > open(2) and openat2(2) to avoid duplicating information such as the list > > of O_* flags or common errors. > > > > In addition to describing all of the key flags, information about the > > extensibility design is provided so that users can better understand why > > they need to pass sizeof(struct open_how) and how their programs will > > work across kernels. After some discussions with David Laight, I also > > included explicit instructions to zero the structure to avoid issues > > when recompiling with new headers. > > > > Signed-off-by: Aleksa Sarai > > Thanks. I've applied this patch, but also done quite a lot of > editing of the page. The current draft is below (and also pushed > to Git). Could I ask you to review the page, to see if I injected > any error during my edits. Looks good to me. > In addition, I've added a number of FIXMEs in comments > in the page source. Can you please check these, and let me > know your thoughts. Will do, see below. > .\" FIXME I find the "previously-functional systems" in the previous > .\" sentence a little odd (since openat2() ia new sysycall), so I would > .\" like to clarify a little... > .\" Are you referring to the scenario where someone might take an > .\" existing application that uses openat() and replaces the uses > .\" of openat() with openat2()? In which case, is it correct to > .\" understand that you mean that one should not just indiscriminately > .\" add the RESOLVE_NO_XDEV flag to all of the openat2() calls? > .\" If I'm not on the right track, could you point me in the right > .\" direction please. This is mostly meant as a warning to hopefully avoid applications because the developer didn't realise that system paths may contain symlinks or bind-mounts. For an application which has switched to openat2() and then uses RESOLVE_NO_SYMLINKS for a non-security reason, it's possible that on some distributions (or future versions of a distribution) that their application will stop working because a system path suddenly contains a symlink or is a bind-mount. This was a concern which was brought up on LWN some time ago. If you can think of a phrasing that makes this more clear, I'd appreciate it. > .\" FIXME: what specific details in symlink(7) are being referred > .\" by the following sentence? It's not clear. The section on magic-links, but you're right that the sentence ordering is a bit odd. It should probably go after the first sentence. > .\" FIXME I found the following hard to understand (in particular, the > .\" meaning of "scoped" is unclear) , and reworded as below. Is it okay? > .\" Absolute symbolic links and ".." path components will be scoped to > .\" .IR dirfd . Scoped does broadly mean "interpreted relative to", though the difference is mainly that when I said scoped it's meant to be more of an assertive claim ("the kernel promises to always treat this path inside dirfd"). But "interpreted relative to" is a clearer way of phrasing the semantics, so I'm okay with this change. > .\" FIXME The next piece is unclear (to me). What kind of ".." escape > .\" attempts does chroot() not detect that RESOLVE_IN_ROOT does? If the root is moved, you can escape from a chroot(2). But this sentence might not really belong in a man-page since it's describing (important) aspects of the implementation and not the semantics. -- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH