ircd::fs: Improve request priority value related; get sysconf info.

include/ircd/fs/fsync.h

@@ -24,6 +24,8 @@ struct ircd::fs::fsync_opts
 {
 	fsync_opts() = default;
 
-	/// Request priority (this option may be improved, avoid for now)
-	int16_t priority {0};
+	/// Request priority. This value is ignored by the kernel for the
+	/// operations provided by this interface. It is still provided for
+	/// consistency and may be used internally by IRCd in the future.
+	int8_t priority {-1};
 };

include/ircd/fs/read.h

@@ -36,8 +36,10 @@ struct ircd::fs::read_opts
 	/// Offset in the file to start the read from.
 	off_t offset {0};
 
-	/// Request priority (this option may be improved, avoid for now)
-	int16_t priority {0};
+	/// Request priority. Higher value request will take priority over lower
+	/// value. Lowest value is zero. Negative value will receive a contextual
+	/// value internally (generally just zero). Default is -1.
+	int8_t priority {-1};
 };
 
 inline

include/ircd/fs/write.h

@@ -47,8 +47,10 @@ struct ircd::fs::write_opts
 	/// Alignment requirement.
 	size_t alignment {0};
 
-	/// Request priority (this option may be improved, avoid for now)
-	int16_t priority {0};
+	/// Request priority. Higher value request will take priority over lower
+	/// value. Lowest value is zero. Negative value will receive a contextual
+	/// value internally (generally just zero). Default is -1.
+	int8_t priority {-1};
 
 	/// for allocate()
 	bool keep_size {false};

include/ircd/info.h

@@ -51,6 +51,7 @@ namespace ircd::info
 
 	extern const int glibc_version[3];
 	extern const string_view glibc_version_str;
+	extern const int aio_reqprio_max;
 	#ifdef HAVE_SYS_UTSNAME_H
 	extern const ::utsname utsname;
 	#endif

ircd/aio.cc

@@ -17,6 +17,7 @@ namespace ircd::fs
 {
 	extern char _zero_pads_[4096];
 	static size_t _zero_pads_required(const size_t &buf_size, const size_t &alignment);
+	static int reqprio(int);
 }
 
 //
@@ -27,7 +28,7 @@ ircd::fs::aio::request::fsync::fsync(const int &fd,
                                      const fsync_opts &opts)
 :request{fd}
 {
-	aio_reqprio = opts.priority;
+	aio_reqprio = reqprio(opts.priority);
 	aio_lio_opcode = IOCB_CMD_FSYNC;
 
 	aio_buf = 0;
@@ -55,7 +56,7 @@ ircd::fs::aio::request::fdsync::fdsync(const int &fd,
                                        const fsync_opts &opts)
 :request{fd}
 {
-	aio_reqprio = opts.priority;
+	aio_reqprio = reqprio(opts.priority);
 	aio_lio_opcode = IOCB_CMD_FDSYNC;
 
 	aio_buf = 0;
@@ -92,7 +93,7 @@ ircd::fs::aio::request::read::read(const int &fd,
 	},
 }
 {
-	aio_reqprio = opts.priority;
+	aio_reqprio = reqprio(opts.priority);
 	aio_lio_opcode = IOCB_CMD_PREADV;
 
 	aio_buf = uintptr_t(iov.data());
@@ -144,7 +145,7 @@ ircd::fs::aio::request::write::write(const int &fd,
 	},
 }}
 {
-	aio_reqprio = opts.priority;
+	aio_reqprio = reqprio(opts.priority);
 	aio_lio_opcode = IOCB_CMD_PWRITEV;
 
 	aio_buf = uintptr_t(iov.data());
@@ -217,6 +218,18 @@ ircd::fs::_zero_pads_required(const size_t &buf_size,
 	return alignment - (buf_size % alignment);
 }
 
+int
+ircd::fs::reqprio(int input)
+{
+	// no use for negative values yet; make them zero.
+	input = std::max(input, 0);
+
+	// value is reduced to system maximum.
+	input = std::min(input, ircd::info::aio_reqprio_max);
+
+	return input;
+}
+
 //
 // aio
 //

ircd/info.cc

@@ -77,11 +77,12 @@ ircd::info::dump()
 	// This message flashes posix information about the resource limits
 	log::debug
 	{
-		"AS=%lu DATA=%lu RSS=%lu NOFILE=%zu",
+		"AS=%lu DATA=%lu RSS=%lu NOFILE=%zu; aio_reqprio_max=%d",
 		rlimit_as,
 		rlimit_data,
 		rlimit_rss,
-		rlimit_nofile
+		rlimit_nofile,
+		aio_reqprio_max
 	};
 }
 
@@ -197,6 +198,14 @@ ircd::info::glibc_version_str
                glibc_version[2])
 );
 
+decltype(ircd::info::aio_reqprio_max)
+ircd::info::aio_reqprio_max
+{
+	#ifdef _SC_AIO_PRIO_DELTA_MAX
+	int(syscall(::sysconf, _SC_AIO_PRIO_DELTA_MAX))
+	#endif
+};
+
 #ifdef HAVE_SYS_UTSNAME_H
 decltype(ircd::info::utsname)
 ircd::info::utsname{[]