ircd::fs: Support various RWF flags for operations; also preadv2().

configure.ac

@@ -711,6 +711,7 @@ AC_CHECK_FUNCS([        \
 	vsnprintf           \
 	posix_fadvise       \
 	pwritev2            \
+	preadv2             \
 ])
 
 AC_SEARCH_LIBS(dlinfo, dl, AC_DEFINE(HAVE_DLINFO, 1, [Define if you have dlinfo]))

include/ircd/fs/aio.h

@@ -30,6 +30,9 @@ namespace ircd::fs::aio
 	extern const bool support_fdsync;
 	extern const bool support_append;
 	extern const bool support_nowait;
+	extern const bool support_hipri;
+	extern const bool support_sync;
+	extern const bool support_dsync;
 
 	extern const size_t MAX_EVENTS;
 	extern const size_t MAX_REQPRIO;

include/ircd/fs/opts.h

@@ -21,10 +21,15 @@ namespace ircd::fs
 /// Options common to all operations
 struct ircd::fs::opts
 {
-    /// Offset in the file.
+	static const int highest_priority;
+
+	/// Offset in the file. If this is -1, for writes, it indicates an append
+	/// at the end of the file (RWF_APPEND or legacy non-atomic lseek()).
 	off_t offset {0};
 
-	/// Request priority. Lower value takes priority over higher.
+	/// Request priority. Lower value takes priority over higher. The lowest
+	/// possible priority value is special, on supporting platforms (RWF_HIPRI).
+	/// One can either simply set the integer minimum or use the extern value.
 	int8_t priority {0};
 
 	/// Submits the I/O request immediately rather than allowing IRCd to
@@ -32,6 +37,13 @@ struct ircd::fs::opts
 	/// (only relevant to aio).
 	bool nodelay {false};
 
+	/// Setting this to false enables non-blocking behavior. If the operation
+	/// would block, EAGAIN is returned. This is only available with RWF_NOWAIT
+	/// on newer systems, otherwise this value is ignored and is always true.
+	/// This feature makes up for the fact that O_NONBLOCK when opening the
+	/// file is ineffective for regular files.
+	bool blocking {true};
+
 	/// Determines whether this operation is conducted via AIO. If not, a
 	/// direct syscall is made. Using AIO will only block one ircd::ctx while
 	/// a direct syscall will block the thread (all contexts). If AIO is not

include/ircd/fs/write.h

@@ -66,6 +66,23 @@ struct ircd::fs::write_opts
 	/// in the useful propagation of an exception for this event.
 	bool interruptible {true};
 
+	/// Whether to update the fd's offset on appends. This happens naturally
+	/// when the file is opened in append mode. If not, we get the same per-
+	/// write atomic seek behavior if RWF_APPEND is supported. In the latter
+	/// case, this option determines whether the fd's offset is affected.
+	bool update_offset {true};
+
+	/// Whether to RWF_SYNC or RWF_DSYNC depending on the metadata option. This
+	/// is a range-sync, it only covers the offset and size of the write;
+	/// perhaps a worthy replacement for sync_file_range(2).
+	bool sync {false};
+
+	/// When sync is true: if metadata is true RWF_SYNC (like fsync(2)) is used,
+	/// otherwise RWF_DSYNC (like fdsync(2)) is used. This is only if available,
+	/// Careful, if it is not available you are responsible for following the
+	/// write with fsync(2)/fdsync(2) yourself.
+	bool metadata {false};
+
 	write_opts(const off_t &);
 	write_opts() = default;
 };

ircd/fs.cc

@@ -408,6 +408,7 @@ ircd::fs::flush(const fd &fd,
 
 namespace ircd::fs
 {
+	static size_t _read(const fd &, const const_iovec_view &, const read_opts &);
 	static size_t read(const fd &, const const_iovec_view &, const read_opts &);
 }
 
@@ -568,7 +569,7 @@ ircd::fs::read(const fd &fd,
 }
 #pragma GCC diagnostic pop
 
-/// Lowest-level read() call. This call only conducts a single operation
+/// Lowest-level'ish read() call. This call only conducts a single operation
 /// (no looping) and can return a partial read(). It does have branches
 /// for various read_opts. The arguments involve `struct ::iovec` which
 /// we do not expose to the ircd.h API; thus this function is internal to
@@ -584,6 +585,38 @@ ircd::fs::read(const fd &fd,
 		return aio::read(fd, iov, opts);
 	#endif
 
+	return _read(fd, iov, opts);
+}
+
+#ifdef HAVE_PREADV2
+size_t
+ircd::fs::_read(const fd &fd,
+                const const_iovec_view &iov,
+                const read_opts &opts)
+{
+	int flags{0};
+
+	if(aio::support_hipri && reqprio(opts.priority) == reqprio(opts::highest_priority))
+		flags |= RWF_HIPRI;
+
+	if(aio::support_nowait && !opts.blocking)
+		flags |= RWF_NOWAIT;
+
+	const auto ret
+	{
+		opts.interruptible?
+			syscall(::preadv2, fd, iov.data(), iov.size(), opts.offset, flags):
+			syscall_nointr(::preadv2, fd, iov.data(), iov.size(), opts.offset, flags)
+	};
+
+	return size_t(ret);
+}
+#else
+size_t
+ircd::fs::_read(const fd &fd,
+                const const_iovec_view &iov,
+                const read_opts &opts)
+{
 	const auto ret
 	{
 		opts.interruptible?
@@ -593,6 +626,7 @@ ircd::fs::read(const fd &fd,
 
 	return size_t(ret);
 }
+#endif // HAVE_PREADV2
 
 ///////////////////////////////////////////////////////////////////////////////
 //
@@ -738,17 +772,39 @@ ircd::fs::append(const string_view &path,
 	return append(fd, bufs, opts);
 }
 
+// When we have pwritev2() we can use RWF_APPEND indicated by
+// the -1. Otherwise, we don't keep flags in userspace and we
+// don't check the fd for whether it was opened with O_APPEND
+// so the user may just have to eat the cost of an extra lseek().
+#ifdef HAVE_PWRITEV2
 size_t
 ircd::fs::append(const fd &fd,
                  const const_buffers &bufs,
                  const write_opts &opts_)
 {
 	auto opts(opts_);
+	if(!aio::support_append)
+	{
 		if(!opts.offset)
 			opts.offset = syscall(::lseek, fd, 0, SEEK_END);
+	}
+	else opts.offset = -1;
+
+	return write(fd, bufs, opts);
+}
+#else
+size_t
+ircd::fs::append(const fd &fd,
+                 const const_buffers &bufs,
+                 const write_opts &opts_)
+{
+	auto opts(opts_);
+	if(!opts.offset || opts.offset == -1)
+		opts.offset = syscall(::lseek, fd, 0, SEEK_END);
 
 	return write(fd, bufs, opts);
 }
+#endif // HAVE_PWRITEV2
 
 ircd::const_buffer
 ircd::fs::write(const string_view &path,
@@ -812,8 +868,8 @@ ircd::fs::write(const fd &fd,
 			info::iov_max
 		};
 
+	size_t off(0);
 	write_opts opts(opts_);
-	size_t off(opts.offset - opts_.offset);
 	assert(bufs.size() <= info::iov_max);
 	struct ::iovec iovbuf[bufs.size()]; do
 	{
@@ -825,9 +881,8 @@ ircd::fs::write(const fd &fd,
 		opts.offset += write(fd, iov, opts);
 		assert(opts.offset >= opts_.offset);
 		off = opts.offset - opts_.offset;
-		assert(off <= buffers::size(bufs));
 	}
-	while(opts.all && off < buffers::size(bufs));
+	while(opts.all && opts_.offset >= 0 && off < buffers::size(bufs));
 	assert(opts.offset >= opts_.offset);
 	assert(ssize_t(off) == opts.offset - opts_.offset);
 	assert(!opts.all || off == buffers::size(bufs));
@@ -862,10 +917,34 @@ ircd::fs::_write(const fd &fd,
 {
 	int flags{0};
 
+	assert(opts.offset >= 0 || aio::support_append);
+	if(aio::support_append && opts.offset == -1)
+		flags |= RWF_APPEND;
+
+	if(aio::support_hipri && reqprio(opts.priority) == reqprio(opts::highest_priority))
+		flags |= RWF_HIPRI;
+
+	if(aio::support_nowait && !opts.blocking)
+		flags |= RWF_NOWAIT;
+
+	if(aio::support_dsync && opts.sync && !opts.metadata)
+		flags |= RWF_DSYNC;
+
+	if(aio::support_sync && opts.sync && opts.metadata)
+		flags |= RWF_SYNC;
+
+	// Manpages sez that when appending with RWF_APPEND, the offset has no
+	// effect on the write; but if the value of the offset is -1 then the
+	// fd's offset is updated, otherwise it is not.
+	const off_t &offset
+	{
+		(flags & RWF_APPEND) && !opts.update_offset? 0 : opts.offset
+	};
+
 	return
 		opts.interruptible?
-			syscall(::pwritev2, fd, iov.data(), iov.size(), opts.offset, flags):
+			syscall(::pwritev2, fd, iov.data(), iov.size(), offset, flags):
-			syscall_nointr(::pwritev2, fd, iov.data(), iov.size(), opts.offset, flags);
+			syscall_nointr(::pwritev2, fd, iov.data(), iov.size(), offset, flags);
 }
 #else
 size_t
@@ -894,21 +973,61 @@ decltype(ircd::fs::aio::support)
 extern __attribute__((weak))
 ircd::fs::aio::support;
 
-decltype(ircd::fs::aio::support_fsync)
+decltype(ircd::fs::aio::support_sync)
 extern __attribute__((weak))
-ircd::fs::aio::support_fsync;
+ircd::fs::aio::support_sync
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 7
+};
 
-decltype(ircd::fs::aio::support_fdsync)
+decltype(ircd::fs::aio::support_dsync)
 extern __attribute__((weak))
-ircd::fs::aio::support_fdsync;
+ircd::fs::aio::support_dsync
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 7
+};
 
-decltype(ircd::fs::aio::support_append)
+decltype(ircd::fs::aio::support_hipri)
 extern __attribute__((weak))
-ircd::fs::aio::support_append;
+ircd::fs::aio::support_hipri
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 6
+};
 
 decltype(ircd::fs::aio::support_nowait)
 extern __attribute__((weak))
-ircd::fs::aio::support_nowait;
+ircd::fs::aio::support_nowait
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 14
+};
+
+decltype(ircd::fs::aio::support_append)
+extern __attribute__((weak))
+ircd::fs::aio::support_append
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 16
+};
+
+decltype(ircd::fs::aio::support_fsync)
+extern __attribute__((weak))
+ircd::fs::aio::support_fsync
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 18
+};
+
+decltype(ircd::fs::aio::support_fdsync)
+extern __attribute__((weak))
+ircd::fs::aio::support_fdsync
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 18
+};
 
 decltype(ircd::fs::aio::MAX_EVENTS)
 extern __attribute__((weak))
@@ -1245,6 +1364,12 @@ decltype(ircd::fs::opts_default)
 ircd::fs::opts_default
 {};
 
+decltype(ircd::fs::opts::highest_priority)
+ircd::fs::opts::highest_priority
+{
+	std::numeric_limits<decltype(priority)>::min()
+};
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // fs/iov.h
@@ -1255,6 +1380,7 @@ ircd::fs::make_iov(const iovec_view &iov,
                    const mutable_buffers &bufs,
                    const size_t &offset)
 {
+	assert(offset <= buffers::size(bufs));
 	const size_t max
 	{
 		std::min(iov.size(), bufs.size())
@@ -1293,6 +1419,7 @@ ircd::fs::make_iov(const iovec_view &iov,
                    const const_buffers &bufs,
                    const size_t &offset)
 {
+	assert(offset <= buffers::size(bufs));
 	const size_t max
 	{
 		std::min(iov.size(), bufs.size())

ircd/fs_aio.cc

@@ -28,7 +28,31 @@ ircd::fs::aio::support
 	true
 };
 
-/// True if RWF_NOWAIT is support by AIO.
+/// True if RWF_SYNC is supported by AIO.
+decltype(ircd::fs::aio::support_sync)
+ircd::fs::aio::support_sync
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 7
+};
+
+/// True if RWF_DSYNC is supported by AIO.
+decltype(ircd::fs::aio::support_dsync)
+ircd::fs::aio::support_dsync
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 7
+};
+
+/// True if RWF_HIPRI is supported by AIO.
+decltype(ircd::fs::aio::support_hipri)
+ircd::fs::aio::support_hipri
+{
+	info::kversion[0] >= 4 &&
+	info::kversion[1] >= 6
+};
+
+/// True if RWF_NOWAIT is supported by AIO.
 decltype(ircd::fs::aio::support_nowait)
 ircd::fs::aio::support_nowait
 {
@@ -36,7 +60,7 @@ ircd::fs::aio::support_nowait
 	info::kversion[1] >= 14
 };
 
-/// True if RWF_APPEND is support by AIO.
+/// True if RWF_APPEND is supported by AIO.
 decltype(ircd::fs::aio::support_append)
 ircd::fs::aio::support_append
 {
@@ -215,6 +239,21 @@ ircd::fs::aio::request::write::write(const int &fd,
 	aio_buf = uintptr_t(iov.data());
 	aio_nbytes = iov.size();
 	aio_offset = opts.offset;
+
+	#ifdef HAVE_PWRITEV2
+	if(aio::support_append && opts.offset == -1)
+	{
+		// AIO departs from pwritev2() behavior and EINVAL's on -1.
+		aio_offset = 0;
+		aio_rw_flags |= RWF_APPEND;
+	}
+
+	if(aio::support_dsync && opts.sync && !opts.metadata)
+		aio_rw_flags |= RWF_DSYNC;
+
+	if(aio::support_sync && opts.sync && opts.metadata)
+		aio_rw_flags |= RWF_SYNC;
+	#endif
 }
 
 size_t
@@ -287,6 +326,14 @@ ircd::fs::aio::request::request(const int &fd,
 	aio_resfd = system->resfd.native_handle();
 	aio_fildes = fd;
 	aio_data = uintptr_t(this);
+
+	#if defined(HAVE_PWRITEV2) && defined(HAVE_PREADV2)
+	if(aio::support_hipri && reqprio(opts->priority) == reqprio(opts::highest_priority))
+		aio_rw_flags |= RWF_HIPRI;
+
+	if(aio::support_nowait && !opts->blocking)
+		aio_rw_flags |= RWF_NOWAIT;
+	#endif
 }
 
 ircd::fs::aio::request::~request()