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‎.gitignore‎

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/build

‎CMakeLists.txt‎

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project(autofsync)
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cmake_minimum_required(VERSION 3.6)
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set(CMAKE_C_STANDARD 99)
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set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wno-unused-parameter")
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set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror=format")
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set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wl,--unresolved-symbols=report-all")
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add_library(autofsync SHARED
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autofsync.c
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)
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set_target_properties(autofsync PROPERTIES PREFIX "")
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target_link_libraries(autofsync PRIVATE ${CMAKE_DL_LIBS})

‎LICENSE‎

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The MIT License (MIT)
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.

‎README.md‎

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autofsync
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=========
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Intercepts `write()` call, and calls `fdatasync()` when certain amount of data
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were written to a file. Limit size is adjusted at run time to keep `fdatasync()`
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durations around predefined value. The goal is to express writeback cache size
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limit in seconds rather than in bytes.
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Library is supposed to be injected into applications with the help of
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`LD_PRELOAD`.

‎autofsync.c‎

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// Copyright © 2018 Rinat Ibragimov
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//
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// This file is part of autofsync.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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#define _GNU_SOURCE
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#include "uthash.h"
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#include <dlfcn.h>
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#include <fcntl.h>
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#include <stdarg.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <time.h>
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#include <unistd.h>
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static const size_t g_dirty_limit_initial = 1024 * 1024;
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static const size_t g_dirty_limit_low = 1024 * 1024;
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static const size_t g_dirty_limit_high = 2ull * 1024 * 1024 * 1024;
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static const double g_target_latency_high = 1.1;
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static const double g_target_latency_low = 0.9;
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#if 0
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#define LOG(fmt, ...) printf("autofsync: " fmt "\n", __VA_ARGS__)
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#define LOG_(fmt) printf("autofsync: " fmt "\n")
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#else
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#define LOG(...)
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#define LOG_(...)
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#endif
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#define unlikely(x) __builtin_expect((x), 0)
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#define WEAK_SYMBOL __attribute__((weak))
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#define ensure_entry_points_initialized() \
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do { \
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if (unlikely(!real_entry_points_initialized)) \
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initialize_real_entry_points(); \
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} while (0)
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#define get_mode() \
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({ \
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int mode; \
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if (__OPEN_NEEDS_MODE(oflag)) { \
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va_list a; \
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va_start(a, oflag); \
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mode = va_arg(a, int); \
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va_end(a); \
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} \
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mode; \
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})
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struct file {
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int fd;
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size_t dirty;
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size_t dirty_limit;
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UT_hash_handle hh;
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};
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static struct file *g_files = NULL;
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static bool real_entry_points_initialized = false;
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static int (*real_open)(const char *fname, int oflag, ...);
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static int (*real_open64)(const char *fname, int oflag, ...);
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static int (*real_openat)(int atfd, const char *fname, int oflag, ...);
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static int (*real_openat64)(int atfd, const char *fname, int oflag, ...);
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static int (*real_close)(int);
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static ssize_t (*real_write)(int, const void *, ssize_t);
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static void
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initialize_real_entry_points(void)
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{
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real_open = dlsym(RTLD_NEXT, "open");
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real_open64 = dlsym(RTLD_NEXT, "open64");
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real_openat = dlsym(RTLD_NEXT, "openat");
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real_openat64 = dlsym(RTLD_NEXT, "openat64");
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real_write = dlsym(RTLD_NEXT, "write");
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real_close = dlsym(RTLD_NEXT, "close");
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real_entry_points_initialized = true;
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}
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static size_t
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align_4k(size_t sz)
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{
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return sz / 4096 * 4096;
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}
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static void
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account_opened_fd(int fd)
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{
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struct stat sb;
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int ret = fstat(fd, &sb);
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if (ret != 0)
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return;
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if (!S_ISREG(sb.st_mode))
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return;
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struct file *new_file = calloc(sizeof(*new_file), 1);
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if (!new_file)
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return;
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new_file->fd = fd;
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new_file->dirty_limit = g_dirty_limit_initial;
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new_file->dirty = 0;
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struct file *old_file = NULL;
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HASH_REPLACE_INT(g_files, fd, new_file, old_file);
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if (old_file != NULL) {
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LOG_(" unexpected old_file");
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free(old_file);
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}
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}
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static int
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do_open(int (*open_func)(const char *fname, int oflag, ...), const char *fname,
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int oflag, int mode)
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{
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int fd = open_func(fname, oflag, mode);
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if (fd == -1)
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return -1;
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account_opened_fd(fd);
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return fd;
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}
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static int
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do_openat(int (*open_func)(int atfd, const char *fname, int oflag, ...),
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int atfd, const char *fname, int oflag, int mode)
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{
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int fd = open_func(atfd, fname, oflag, mode);
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if (fd == -1)
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return -1;
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account_opened_fd(fd);
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return fd;
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}
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WEAK_SYMBOL
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int
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open(const char *fname, int oflag, ...)
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{
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int mode = get_mode();
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LOG("open: fname=%s, oflag=%d, mode=%d", fname, oflag, mode);
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ensure_entry_points_initialized();
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return do_open(real_open, fname, oflag, mode);
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}
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WEAK_SYMBOL
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int
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open64(const char *fname, int oflag, ...)
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{
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int mode = get_mode();
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LOG("open64: fname=%s, oflag=%d, mode=%d", fname, oflag, mode);
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ensure_entry_points_initialized();
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return do_open(real_open64, fname, oflag, mode);
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}
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WEAK_SYMBOL
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int
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openat(int atfd, const char *fname, int oflag, ...)
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{
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int mode = get_mode();
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LOG("openat: atfd=%d, fname=%s, oflag=%d, mode=%d", atfd, fname, oflag,
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mode);
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ensure_entry_points_initialized();
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return do_openat(real_openat, atfd, fname, oflag, mode);
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}
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WEAK_SYMBOL
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int
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openat64(int atfd, const char *fname, int oflag, ...)
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{
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int mode = get_mode();
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LOG("openat64: atfd=%d, fname=%s, oflag=%d, mode=%d", atfd, fname, oflag,
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mode);
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ensure_entry_points_initialized();
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return do_openat(real_openat64, atfd, fname, oflag, mode);
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}
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WEAK_SYMBOL
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int
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close(int fd)
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{
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LOG("close: fd = %d", fd);
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ensure_entry_points_initialized();
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struct file *a_file = NULL;
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HASH_FIND_INT(g_files, &fd, a_file);
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if (a_file) {
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HASH_DEL(g_files, a_file);
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free(a_file);
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} else {
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LOG_(" mismatched close");
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}
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return real_close(fd);
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}
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static void
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write_throttle(int fd, ssize_t bytes_written)
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{
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struct file *a_file = NULL;
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HASH_FIND_INT(g_files, &fd, a_file);
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if (a_file == NULL)
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return;
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a_file->dirty += bytes_written;
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LOG(" dirty = %zu, dirty_limit = %zu", a_file->dirty, a_file->dirty_limit);
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if (a_file->dirty < a_file->dirty_limit)
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return;
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a_file->dirty = 0;
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struct timespec t1;
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if (clock_gettime(CLOCK_MONOTONIC, &t1) != 0)
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return;
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if (fdatasync(fd) != 0)
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return;
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struct timespec t2;
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if (clock_gettime(CLOCK_MONOTONIC, &t2) != 0)
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return;
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double elapsed = t2.tv_sec - t1.tv_sec + (t2.tv_nsec - t1.tv_nsec) * 1e-9;
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LOG(" fdatasync took %f seconds", elapsed);
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if (elapsed > g_target_latency_high) {
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double slowdown = elapsed / g_target_latency_high;
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LOG(" slowdown = %f", slowdown);
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if (slowdown > 2) {
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a_file->dirty_limit /= slowdown;
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} else {
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a_file->dirty_limit *= 0.7;
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}
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if (a_file->dirty_limit < g_dirty_limit_low)
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a_file->dirty_limit = g_dirty_limit_low;
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a_file->dirty_limit = align_4k(a_file->dirty_limit);
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LOG(" decreasing dirty_limit to %zu", a_file->dirty_limit);
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} else if (elapsed < g_target_latency_low) {
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a_file->dirty_limit *= 1.3;
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if (a_file->dirty_limit > g_dirty_limit_high)
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a_file->dirty_limit = g_dirty_limit_high;
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a_file->dirty_limit = align_4k(a_file->dirty_limit);
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LOG(" increasing dirty_limit to %zu", a_file->dirty_limit);
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}
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}
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WEAK_SYMBOL
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ssize_t
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write(int fd, const void *buf, size_t count)
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{
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LOG("write: fd = %d, buf = %p, count = %zu", fd, buf, count);
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ensure_entry_points_initialized();
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const ssize_t bytes_written = real_write(fd, buf, count);
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if (bytes_written == -1)
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return -1;
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write_throttle(fd, bytes_written);
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return bytes_written;
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}

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