[HEADSUP] Disallowing read() of a directory fd

[Brooks Davis]

On Thu, May 14, 2020 at 01:26:46PM -0500, Kyle Evans wrote:
> Hi,
> 
> This is a heads up, given that I'm completely flipping our historical
> behavior- I intend to commit this review in a couple days' time
> without substantial objection: https://reviews.freebsd.org/D24596
> 
> With this, FreeBSD 13 will not allow read() of a directory fd, which
> could have previously returned some data from the underlying
> filesystem in no particular standardized format.
> 
> This is a still-standards-compliant switch from one
> implementation-defined behavior to another that's already been adopted
> in various other popular kernels, to include OpenBSD, MacOS, and
> Linux.
> 
> Worth noting is that there's not really one largely-compelling reasons
> to switch this after so many years (unless you find yourself that
> irate when you accidentally `cat` a directory), but there are some
> benefits which are briefly discussed in the commentary around the
> review along with the history of the current behavior.
> 
> This change also simplifies filesystem implementations to some extent.

I'm sure this made sense in v7, but I've never opened a directory with vi
or cat and thought "that's what I wanted to do".

In theory can use it as a terrible ls I've you've totally foobar'd your
system, but we have /rescue these days.

-- Brooks
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