[Libguestfs] [PATCH nbdkit 1/2] file: Add an internal "mode"

[Laszlo Ersek]

On 08/18/22 11:53, Richard W.M. Jones wrote:
> 
> This is upstream in 5 commits 5764fa6f4..dd28b0054:
> 
> https://gitlab.com/nbdkit/nbdkit/-/commit/2620d95a4585204f0db0d55c0d41276d11970436
> https://gitlab.com/nbdkit/nbdkit/-/commit/185e7d4010b353f36b5ca5d47467a770c530e58c
> https://gitlab.com/nbdkit/nbdkit/-/commit/17655b1ca67caa454e7a4ac83bc8c052b79a692d
> https://gitlab.com/nbdkit/nbdkit/-/commit/e7fdffde8142fb083625678b7a55455751185502
> https://gitlab.com/nbdkit/nbdkit/-/commit/dd28b005430d020ccd1825437937c317332d3007
> 
> This also includes dirfd functionality and a rather complicated test
> for that.  Turns out that bash refuses to open a directory as a file
> descriptor :-(

This doesn't match my experience; for me, bash opens e.g. /tmp just fine
on both RHEL7 and Fedora35 -- but it must be a read-only open.

$ exec 9</tmp
[ok]

$ exec 9<>/tmp
bash: /tmp: Is a directory

The latter is actually expected; it comes from open(). See EISDIR at
<https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html>.

Commit dd28b005430d also adds

  dfd = open (tmpdir, O_RDONLY | O_DIRECTORY);

where I think O_DIRECTORY is not strictly necessary (per spec, because
O_CREAT is absent, O_DIRECTORY only helps us refuse a non-directory --
but we do not expect such "attacks" here). So my take is that
O_DIRECTORY could be dropped from the C code, at which point a bash
redirection (read-only) should work just the same.

Laszlo