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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 bytecodealliance#516. [filetime]: https://github.com/alexcrichton/filetime
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Jakub Konka
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Nov 10, 2019
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,104 @@ | ||
| use super::super::filetime::FileTime; | ||
| use cfg_if::cfg_if; | ||
| use std::ffi::CStr; | ||
| use std::fs::File; | ||
| use std::io; | ||
| use std::sync::atomic::{AtomicUsize, Ordering::SeqCst}; | ||
|
|
||
| cfg_if! { | ||
| if #[cfg(any( | ||
| target_os = "macos", | ||
| target_os = "freebsd", | ||
| target_os = "ios", | ||
| target_os = "dragonfly" | ||
| ))] { | ||
| pub(crate) const UTIME_NOW: i64 = -1; | ||
| } else if #[cfg(target_os = "openbsd")] { | ||
| // https://github.com/openbsd/src/blob/master/sys/sys/stat.h#L187 | ||
| pub(crate) const UTIME_NOW: i64 = -2; | ||
| } else if #[cfg(target_os = "netbsd" )] { | ||
| // http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/sys/stat.h?rev=1.69&content-type=text/x-cvsweb-markup&only_with_tag=MAIN | ||
| pub(crate) const UTIME_NOW: i64 = 1_073_741_823; | ||
| } | ||
| } | ||
|
|
||
| cfg_if! { | ||
| if #[cfg(any( | ||
| target_os = "macos", | ||
| target_os = "freebsd", | ||
| target_os = "ios", | ||
| target_os = "dragonfly" | ||
| ))] { | ||
| pub(crate) const UTIME_OMIT: i64 = -2; | ||
| } else if #[cfg(target_os = "openbsd")] { | ||
| // https://github.com/openbsd/src/blob/master/sys/sys/stat.h#L187 | ||
| pub(crate) const UTIME_OMIT: i64 = -1; | ||
| } else if #[cfg(target_os = "netbsd")] { | ||
| // http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/sys/stat.h?rev=1.69&content-type=text/x-cvsweb-markup&only_with_tag=MAIN | ||
| pub(crate) const UTIME_OMIT: i64 = 1_073_741_822; | ||
| } | ||
| } | ||
|
|
||
| pub(crate) fn utimensat( | ||
| dirfd: &File, | ||
| path: &str, | ||
| atime: FileTime, | ||
| mtime: FileTime, | ||
| symlink: bool, | ||
| ) -> io::Result<()> { | ||
| use super::super::filetime::{to_timespec, utimesat}; | ||
| use std::ffi::CString; | ||
| use std::os::unix::prelude::*; | ||
|
|
||
| // Attempt to use the `utimensat` syscall, but if it's not supported by the | ||
| // current kernel then fall back to an older syscall. | ||
| if let Some(func) = fetch_utimensat() { | ||
| let flags = if symlink { | ||
| libc::AT_SYMLINK_NOFOLLOW | ||
| } else { | ||
| 0 | ||
| }; | ||
|
|
||
| let p = CString::new(path.as_bytes())?; | ||
| let times = [to_timespec(&atime), to_timespec(&mtime)]; | ||
| let rc = unsafe { func(dirfd.as_raw_fd(), p.as_ptr(), times.as_ptr(), flags) }; | ||
| if rc == 0 { | ||
| return Ok(()); | ||
| } else { | ||
| return Err(io::Error::last_os_error()); | ||
| } | ||
| } | ||
|
|
||
| utimesat(dirfd, path, atime, mtime, symlink) | ||
| } | ||
|
|
||
| fn fetch_utimensat() -> Option< | ||
| unsafe extern "C" fn( | ||
| libc::c_int, | ||
| *const libc::c_char, | ||
| *const libc::timespec, | ||
| libc::c_int, | ||
| ) -> libc::c_int, | ||
| > { | ||
| static ADDR: AtomicUsize = AtomicUsize::new(0); | ||
| unsafe { | ||
| fetch(&ADDR, CStr::from_bytes_with_nul_unchecked(b"utimensat\0")) | ||
| .map(|sym| std::mem::transmute(sym)) | ||
| } | ||
| } | ||
|
|
||
| fn fetch(cache: &AtomicUsize, name: &CStr) -> Option<usize> { | ||
| match cache.load(SeqCst) { | ||
| 0 => {} | ||
| 1 => return None, | ||
| n => return Some(n), | ||
| } | ||
| let sym = unsafe { libc::dlsym(libc::RTLD_DEFAULT, name.as_ptr() as *const _) }; | ||
| let (val, ret) = if sym.is_null() { | ||
| (1, None) | ||
| } else { | ||
| (sym as usize, Some(sym as usize)) | ||
| }; | ||
| cache.store(val, SeqCst); | ||
| return ret; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,110 @@ | ||
| use std::fs::{self, File}; | ||
| use std::io; | ||
|
|
||
| cfg_if::cfg_if! { | ||
| if #[cfg(target_os = "linux")] { | ||
| pub(crate) use super::linux::filetime::*; | ||
| } else if #[cfg(any( | ||
| target_os = "macos", | ||
| target_os = "netbsd", | ||
| target_os = "freebsd", | ||
| target_os = "openbsd", | ||
| target_os = "ios", | ||
| target_os = "dragonfly" | ||
| ))] { | ||
| pub(crate) use super::bsd::filetime::*; | ||
| } | ||
| } | ||
|
|
||
| #[derive(Debug, Copy, Clone)] | ||
| pub(crate) enum FileTime { | ||
| Now, | ||
| Omit, | ||
| FileTime(filetime::FileTime), | ||
| } | ||
|
|
||
| fn get_times( | ||
| atime: FileTime, | ||
| mtime: FileTime, | ||
| current: impl Fn() -> io::Result<fs::Metadata>, | ||
| ) -> io::Result<(filetime::FileTime, filetime::FileTime)> { | ||
| use std::time::SystemTime; | ||
|
|
||
| let atime = match atime { | ||
| FileTime::Now => { | ||
| let time = SystemTime::now(); | ||
| filetime::FileTime::from_system_time(time) | ||
| } | ||
| FileTime::Omit => { | ||
| let meta = current()?; | ||
| filetime::FileTime::from_last_access_time(&meta) | ||
| } | ||
| FileTime::FileTime(ft) => ft, | ||
| }; | ||
|
|
||
| let mtime = match mtime { | ||
| FileTime::Now => { | ||
| let time = SystemTime::now(); | ||
| filetime::FileTime::from_system_time(time) | ||
| } | ||
| FileTime::Omit => { | ||
| let meta = current()?; | ||
| filetime::FileTime::from_last_modification_time(&meta) | ||
| } | ||
| FileTime::FileTime(ft) => ft, | ||
| }; | ||
|
|
||
| Ok((atime, mtime)) | ||
| } | ||
|
|
||
| pub(crate) fn utimesat( | ||
| dirfd: &File, | ||
| path: &str, | ||
| atime: FileTime, | ||
| mtime: FileTime, | ||
| symlink: bool, | ||
| ) -> io::Result<()> { | ||
| use std::ffi::CString; | ||
| use std::os::unix::prelude::*; | ||
| // emulate *at syscall by reading the path from a combination of | ||
| // (fd, path) | ||
| let p = CString::new(path.as_bytes())?; | ||
| let mut flags = libc::O_RDWR; | ||
| if !symlink { | ||
| flags |= libc::O_NOFOLLOW; | ||
| } | ||
| let fd = unsafe { libc::openat(dirfd.as_raw_fd(), p.as_ptr(), flags) }; | ||
| let f = unsafe { File::from_raw_fd(fd) }; | ||
| let (atime, mtime) = get_times(atime, mtime, || f.metadata())?; | ||
| let times = [to_timeval(atime), to_timeval(mtime)]; | ||
| let rc = unsafe { libc::futimes(f.as_raw_fd(), times.as_ptr()) }; | ||
| return if rc == 0 { | ||
| Ok(()) | ||
| } else { | ||
| Err(io::Error::last_os_error()) | ||
| }; | ||
| } | ||
|
|
||
| fn to_timeval(ft: filetime::FileTime) -> libc::timeval { | ||
| libc::timeval { | ||
| tv_sec: ft.seconds(), | ||
| tv_usec: (ft.nanoseconds() / 1000) as libc::suseconds_t, | ||
| } | ||
| } | ||
|
|
||
| pub(crate) fn to_timespec(ft: &FileTime) -> libc::timespec { | ||
| match ft { | ||
| FileTime::Now => libc::timespec { | ||
| tv_sec: 0, | ||
| tv_nsec: UTIME_NOW, | ||
| }, | ||
| FileTime::Omit => libc::timespec { | ||
| tv_sec: 0, | ||
| tv_nsec: UTIME_OMIT, | ||
| }, | ||
| FileTime::FileTime(ft) => libc::timespec { | ||
| tv_sec: ft.seconds(), | ||
| tv_nsec: ft.nanoseconds() as _, | ||
| }, | ||
| } | ||
| } |
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