On Thu, Oct 3, 2019 at 4:56 PM Aleksa Sarai <cyphar@xxxxxxxxxx> wrote: > Traditionally, magic-links have not been a well-understood topic in > Linux. Given the new changes in their semantics (related to the link > mode of trailing magic-links), it seems like a good opportunity to shine > more light on magic-links and their semantics. [...] > +++ b/man7/symlink.7 > @@ -84,6 +84,25 @@ as they are implemented on Linux and other systems, > are outlined here. > It is important that site-local applications also conform to these rules, > so that the user interface can be as consistent as possible. > +.SS Magic-links > +There is a special class of symlink-like objects known as "magic-links" which I think names like that normally aren't hypenated in english, and instead of "magic-links", it'd be "magic links"? Just like how you wouldn't write "symbolic-link", but "symbolic link". But this is bikeshedding, and if you disagree, feel free to ignore this comment. > +can be found in certain pseudo-filesystems such as > +.BR proc (5) > +(examples include > +.IR /proc/[pid]/exe " and " /proc/[pid]/fd/* .) > +Unlike normal symlinks, magic-links are not resolved through nit: AFAICS symlinks are always referred to as "symbolic links" throughout the manpages. > +pathname-expansion, but instead act as direct references to the kernel's own > +representation of a file handle. As such, these magic-links allow users to > +access files which cannot be referenced with normal paths (such as unlinked > +files still referenced by a running program.) Could maybe add "and files in different mount namespaces" as another example here; at least for me, that's the main usecases for /proc/*/root. [...] > +However, magic-links do not follow this rule. They can have a non-0777 mode, > +which is used for permission checks when the final > +component of an > +.BR open (2)'s Maybe leave out the "open" part, since the same restriction has to also apply to other syscalls operating on files, like truncate() and so on? > +path is a magic-link (see > +.BR path_resolution (7).)
