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Dynamically load utimensat if exists on the host (#535)

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* Dynamically load utimensat if exists on the host

This commit introduces a change to file time management for *nix based
hosts in that it firstly tries to load `utimensat` symbol, and if it
doesn't exist, then falls back to `utimes` instead. This change is
borrowing very heavily from [filetime] crate, however, it introduces a
couple of helpers and methods specific to WASI use case (or more
generally, to a use case which requires modifying times of entities
specified by a pair `(DirFD, RelativePath)` rather than the typical
file time specification based only absolute path or raw file descriptor
as is the case with [filetime] crate. The trick here is, that on kernels
which do not have `utimensat` symbol, this implementation emulates this
behaviour by a combination of `openat` and `utimes`.

This commit also is meant to address #516.

[filetime]: https://github.com/alexcrichton/filetime

* Fix symlink NOFOLLOW flag setting

* Add docs and specify UTIME_NOW/OMIT on Linux

Previously, we relied on [libc] crate for `UTIME_NOW` and `UTIME_OMIT`
constants on Linux. However, following the convention assumed in
[filetime] crate, this is now changed to directly specified by us
in our crate.

[libc]: https://github.com/rust-lang/libc
[filetime]: https://github.com/alexcrichton/filetime

* Refactor UTIME_NOW/OMIT for BSD

* Address final discussion points
This commit is contained in:
Jakub Konka
2019-11-11 18:42:28 +01:00
committed by Alex Crichton
parent 5a1845b4ca
commit 0006a2af95
8 changed files with 335 additions and 103 deletions
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55
crates/wasi-common/src/sys/unix/hostcalls_impl/fs.rs
View File

@@ -1,6 +1,5 @@
#![allow(non_camel_case_types)]
#![allow(unused_unsafe)]
use super::fs_helpers::*;
use crate::helpers::systemtime_to_timestamp;
use crate::hostcalls_impl::{FileType, PathGet};
use crate::sys::host_impl;
@@ -281,25 +280,8 @@ pub(crate) fn path_filestat_set_times(
st_mtim: wasi::__wasi_timestamp_t,
fst_flags: wasi::__wasi_fstflags_t,
) -> Result<()> {
use nix::sys::stat::{utimensat, UtimensatFlags};
use nix::sys::time::{TimeSpec, TimeValLike};
// FIXME this should be a part of nix
fn timespec_omit() -> TimeSpec {
let raw_ts = libc::timespec {
tv_sec: 0,
tv_nsec: utime_omit(),
};
unsafe { std::mem::transmute(raw_ts) }
};
fn timespec_now() -> TimeSpec {
let raw_ts = libc::timespec {
tv_sec: 0,
tv_nsec: utime_now(),
};
unsafe { std::mem::transmute(raw_ts) }
};
use super::super::filetime::*;
use std::time::{Duration, UNIX_EPOCH};
let set_atim = fst_flags & wasi::__WASI_FILESTAT_SET_ATIM != 0;
let set_atim_now = fst_flags & wasi::__WASI_FILESTAT_SET_ATIM_NOW != 0;
@@ -310,31 +292,32 @@ pub(crate) fn path_filestat_set_times(
return Err(Error::EINVAL);
}
let atflags = match dirflags {
wasi::__WASI_LOOKUP_SYMLINK_FOLLOW => UtimensatFlags::FollowSymlink,
_ => UtimensatFlags::NoFollowSymlink,
};
let symlink_nofollow = wasi::__WASI_LOOKUP_SYMLINK_FOLLOW != dirflags;
let atim = if set_atim {
let st_atim = st_atim.try_into()?;
TimeSpec::nanoseconds(st_atim)
let time = UNIX_EPOCH + Duration::from_nanos(st_atim);
FileTime::FileTime(filetime::FileTime::from_system_time(time))
} else if set_atim_now {
timespec_now()
FileTime::Now
} else {
timespec_omit()
FileTime::Omit
};
let mtim = if set_mtim {
let st_mtim = st_mtim.try_into()?;
TimeSpec::nanoseconds(st_mtim)
let time = UNIX_EPOCH + Duration::from_nanos(st_mtim);
FileTime::FileTime(filetime::FileTime::from_system_time(time))
} else if set_mtim_now {
timespec_now()
FileTime::Now
} else {
timespec_omit()
FileTime::Omit
};
let fd = resolved.dirfd().as_raw_fd().into();
utimensat(fd, resolved.path(), &atim, &mtim, atflags).map_err(Into::into)
utimensat(
resolved.dirfd(),
resolved.path(),
atim,
mtim,
symlink_nofollow,
)
.map_err(Into::into)
}
pub(crate) fn path_remove_directory(resolved: PathGet) -> Result<()> {