Some filesystems, such as ZFS, do not report atime. It's pretty useless
in general, so make it an optional field in File.Stat.
Also take the opportunity to make setting timestamps API more flexible
and match the APIs widely available, which have UTIME_OMIT and UTIME_NOW
constants that can be independently set for both fields.
This is needed to handle smoothly the case when atime is null.
There's a good argument to not have this in the std lib but it's more
work to remove it than to leave it in, and this branch is already
20,000+ lines changed.
* std.option allows overriding the debug Io instance
* if the default is used, start code initializes environ and argv0
also fix some places that needed recancel(), thanks mlugg!
See #30562
This is needed unfortunately for OpenBSD and Haiku for process
executable path.
I made it so that you can omit the options usually, but you get a
compile error if you omit the options on those targets.
* policy is to always handle EINTR from all syscalls
* assert the result of realpath
* don't ignore errors from realpath
* hard-code path separators for code simplicity
It's better to avoid references to this global variable, but, in the
cases where it's needed, such as in std.debug.print and collecting stack
traces, better to share the same instance.
Stephen Gregoratto (original author of the fallback) says:
I read through both libcs again to compare:
Musl:
- `stat` path. Check error.
- If path is a symlink, return `OPNOTSUPP`.
- `openat` path as `O_PATH|O_NOFOLLOW|O_CLOEXEC`. Return `OPNOTSUPP` if we got `ELOOP`.
- Build procfs filename.
- `stat` procfs file.
- If procfs file is a symlink, return `OPNOTSUPP`.
- close path fd.
Glibc:
- open path as `O_PATH|O_NOFOLLOW|O_CLOEXEC`.
- fstatat path fd.
- If path is a symlink, return `OPNOTSUPP`.
- Build procfs filename.
- chmod procfs filename. Return `OPNOTSUPP` if we got `ENOENT`.
- close path fd.
I prefer glibc since you open the path first, which avoids a possible
TOCTOU race.
The only known situation in which this occurs is when using musl with
the undocumented extension PTHREAD_CANCEL_MASKED, causing the next
syscall to return ECANCELED.
However zig std lib does not use this mechanism, even when targeting
musl libc because it would require each async task to be on a fresh
pthread.
For the same reason, if third party code were to cause ECANCELED to be
returned from any of these syscalls, it would cause subsequent tasks to
be incorrectly canceled since they cannot be rearmed.
Thus, this Io implementation cannot handle this error code correctly,
expecting never to receive it.
At first I thought about keeping this as an assertion but I can see this
being useful if you already know how many bytes to read and you are
filling the end of the buffer.
This also more closely mirrors POSIX APIs.
Andrew Kelley