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Add support for utimensat as an alternative to lutimes

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OpenBSD doesn't support `lutimes`, but does support `utimensat` which
subsumes it. In fact, all the BSDs, Linux, and newer macOS all support
it. So lets make this our first choice for the implementation.

In addition, let's get rid of the `lutimes` `ENOSYS` special case. The
Linux manpage says

> ENOSYS
>
> The kernel does not support this call; Linux 2.6.22 or later is
> required.

which I think is the origin of this check, but that's a very old version
of Linux at this point. The code can be simplified a lot of we drop
support for it here (as we've done elsewhere, anyways).

Co-Authored-By: John Ericson <John.Ericson@Obsidian.Systems>
This commit is contained in:
Artemis Tosini 2024-10-26 17:12:06 +00:00
parent 3db75b0060
commit d023202811
No known key found for this signature in database
GPG Key ID: EE5227935FE3FF18
3 changed files with 43 additions and 38 deletions
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7
configure.ac
View File

@ -89,9 +89,10 @@ AC_LANG_POP(C++)
AC_CHECK_FUNCS([statvfs pipe2 close_range])
# Check for lutimes, optionally used for changing the mtime of
# symlinks.
AC_CHECK_FUNCS([lutimes])
# Check for lutimes and utimensat, optionally used for changing the
# mtime of symlinks.
AC_CHECK_DECLS([AT_SYMLINK_NOFOLLOW], [], [], [[#include <fcntl.h>]])
AC_CHECK_FUNCS([lutimes utimensat])
# Check whether the store optimiser can optimise symlinks.

70
src/libutil/file-system.cc
View File

@ -630,7 +630,28 @@ void setWriteTime(
time_t modificationTime,
std::optional<bool> optIsSymlink)
{
#ifndef _WIN32
#ifdef _WIN32
// FIXME use `fs::last_write_time`.
//
// Would be nice to use std::filesystem unconditionally, but
// doesn't support access time just modification time.
//
// System clock vs File clock issues also make that annoying.
warn("Changing file times is not yet implemented on Windows, path is '%s'", path);
#elif HAVE_UTIMENSAT && HAVE_DECL_AT_SYMLINK_NOFOLLOW
struct timespec times[2] = {
{
.tv_sec = accessedTime,
.tv_nsec = 0,
},
{
.tv_sec = modificationTime,
.tv_nsec = 0,
},
};
if (utimensat(AT_FDCWD, path.c_str(), times, AT_SYMLINK_NOFOLLOW) == -1)
throw SysError("changing modification time of '%s' (using `utimensat`)", path);
#else
struct timeval times[2] = {
{
.tv_sec = accessedTime,
@ -641,42 +662,21 @@ void setWriteTime(
.tv_usec = 0,
},
};
#endif
auto nonSymlink = [&]{
bool isSymlink = optIsSymlink
? *optIsSymlink
: fs::is_symlink(path);
if (!isSymlink) {
#ifdef _WIN32
// FIXME use `fs::last_write_time`.
//
// Would be nice to use std::filesystem unconditionally, but
// doesn't support access time just modification time.
//
// System clock vs File clock issues also make that annoying.
warn("Changing file times is not yet implemented on Windows, path is '%s'", path);
#else
if (utimes(path.c_str(), times) == -1) {
throw SysError("changing modification time of '%s' (not a symlink)", path);
}
#endif
} else {
throw Error("Cannot modification time of symlink '%s'", path);
}
};
#if HAVE_LUTIMES
if (lutimes(path.c_str(), times) == -1) {
if (errno == ENOSYS)
nonSymlink();
else
throw SysError("changing modification time of '%s'", path);
}
if (lutimes(path.c_str(), times) == -1)
throw SysError("changing modification time of '%s'", path);
#else
nonSymlink();
bool isSymlink = optIsSymlink
? *optIsSymlink
: fs::is_symlink(path);
if (!isSymlink) {
if (utimes(path.c_str(), times) == -1)
throw SysError("changing modification time of '%s' (not a symlink)", path);
} else {
throw Error("Cannot modification time of symlink '%s'", path);
}
#endif
#endif
}

4
src/libutil/meson.build
View File

@ -42,6 +42,8 @@ check_funcs = [
# Optionally used to try to close more file descriptors (e.g. before
# forking) on Unix.
'sysconf',
# Optionally used for changing the mtime of files and symlinks.
'utimensat',
]
foreach funcspec : check_funcs
define_name = 'HAVE_' + funcspec.underscorify().to_upper()
@ -49,6 +51,8 @@ foreach funcspec : check_funcs
configdata.set(define_name, define_value)
endforeach
configdata.set('HAVE_DECL_AT_SYMLINK_NOFOLLOW', cxx.has_header_symbol('fcntl.h', 'AT_SYMLINK_NOFOLLOW').to_int())
subdir('build-utils-meson/threads')
# Check if -latomic is needed