It is frequently useful to sync a single file system, instead of all mounted file systems via sync(2): - On machines with many mounts, it is not at all uncommon for some of them to hang (e.g. unresponsive NFS server). sync(2) will get stuck on those and may never get to the one you do care about (e.g., /). - Some applications write lots of data to the file system and then want to make sure it is flushed to disk. Calling fsync(2) on each file introduces unnecessary ordering constraints that result in a large amount of sub-optimal writeback/flush/commit behavior by the file system. There are currently two ways (that I know of) to sync a single super_block: - BLKFLSBUF ioctl on the block device: That also invalidates the bdev mapping, which isn't usually desirable, and doesn't work for non-block file systems. - 'mount -o remount,rw' will call sync_filesystem as an artifact of the current implemention. Relying on this little-known side effect for something like data safety sounds foolish. Both of these approaches require root privileges, which some applications do not have (nor should they need?) given that sync(2) is an unprivileged operation. This patch introduces a new system call syncfs(2) that takes an fd and syncs only the file system it references. Maybe someday we can $ sync /some/path and not get sync: ignoring all arguments The syscall is motivated by comments by Al and Christoph at the last LSF. syncfs(2) seems like an appropriate name given statfs(2). A similar ioctl was also proposed a while back, see http://marc.info/?l=linux-fsdevel&m=127970513829285&w=2 Signed-off-by: Sage Weil <sage@xxxxxxxxxxxx> --- ChangeLog: v3: Update include/linux/syscalls.h and asm-generic/unistd.h v2: Rename to syncfs, simplify to just take an fd. v1: syncat arch/x86/ia32/ia32entry.S | 1 + arch/x86/include/asm/unistd_32.h | 3 ++- arch/x86/include/asm/unistd_64.h | 2 ++ arch/x86/kernel/syscall_table_32.S | 1 + fs/sync.c | 24 ++++++++++++++++++++++++ include/asm-generic/unistd.h | 4 +++- include/linux/syscalls.h | 1 + 7 files changed, 34 insertions(+), 2 deletions(-) diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index 518bb99..24082b8 100644 --- a/arch/x86/ia32/ia32entry.S +++ b/arch/x86/ia32/ia32entry.S @@ -851,4 +851,5 @@ ia32_sys_call_table: .quad sys_fanotify_init .quad sys32_fanotify_mark .quad sys_prlimit64 /* 340 */ + .quad sys_syncfs ia32_syscall_end: diff --git a/arch/x86/include/asm/unistd_32.h b/arch/x86/include/asm/unistd_32.h index b766a5e..da3903f 100644 --- a/arch/x86/include/asm/unistd_32.h +++ b/arch/x86/include/asm/unistd_32.h @@ -346,10 +346,11 @@ #define __NR_fanotify_init 338 #define __NR_fanotify_mark 339 #define __NR_prlimit64 340 +#define __NR_syncfs 341 #ifdef __KERNEL__ -#define NR_syscalls 341 +#define NR_syscalls 342 #define __ARCH_WANT_IPC_PARSE_VERSION #define __ARCH_WANT_OLD_READDIR diff --git a/arch/x86/include/asm/unistd_64.h b/arch/x86/include/asm/unistd_64.h index 363e9b8..a2e7516 100644 --- a/arch/x86/include/asm/unistd_64.h +++ b/arch/x86/include/asm/unistd_64.h @@ -669,6 +669,8 @@ __SYSCALL(__NR_fanotify_init, sys_fanotify_init) __SYSCALL(__NR_fanotify_mark, sys_fanotify_mark) #define __NR_prlimit64 302 __SYSCALL(__NR_prlimit64, sys_prlimit64) +#define __NR_syncfs 303 +__SYSCALL(__NR_syncfs, sys_syncfs) #ifndef __NO_STUBS #define __ARCH_WANT_OLD_READDIR diff --git a/arch/x86/kernel/syscall_table_32.S b/arch/x86/kernel/syscall_table_32.S index b35786d..d40bd16 100644 --- a/arch/x86/kernel/syscall_table_32.S +++ b/arch/x86/kernel/syscall_table_32.S @@ -340,3 +340,4 @@ ENTRY(sys_call_table) .long sys_fanotify_init .long sys_fanotify_mark .long sys_prlimit64 /* 340 */ + .long sys_syncfs diff --git a/fs/sync.c b/fs/sync.c index ba76b96..92ca208 100644 --- a/fs/sync.c +++ b/fs/sync.c @@ -7,6 +7,7 @@ #include <linux/fs.h> #include <linux/slab.h> #include <linux/module.h> +#include <linux/namei.h> #include <linux/sched.h> #include <linux/writeback.h> #include <linux/syscalls.h> @@ -128,6 +129,29 @@ void emergency_sync(void) } } +/* + * sync a single super + */ +SYSCALL_DEFINE1(syncfs, int, fd) +{ + struct file *file; + struct super_block *sb; + int ret; + int fput_needed; + + file = fget_light(fd, &fput_needed); + if (!file) + return -EBADF; + sb = file->f_dentry->d_sb; + + down_read(&sb->s_umount); + ret = sync_filesystem(sb); + up_read(&sb->s_umount); + + fput_light(file, fput_needed); + return ret; +} + /** * vfs_fsync_range - helper to sync a range of data & metadata to disk * @file: file to sync diff --git a/include/asm-generic/unistd.h b/include/asm-generic/unistd.h index b969770..3cf62eb 100644 --- a/include/asm-generic/unistd.h +++ b/include/asm-generic/unistd.h @@ -646,9 +646,11 @@ __SYSCALL(__NR_prlimit64, sys_prlimit64) __SYSCALL(__NR_fanotify_init, sys_fanotify_init) #define __NR_fanotify_mark 263 __SYSCALL(__NR_fanotify_mark, sys_fanotify_mark) +#define __NR_syncfs 264 +__SYSCALL(__NR_syncfs, sys_syncfs) #undef __NR_syscalls -#define __NR_syscalls 264 +#define __NR_syscalls 265 /* * All syscalls below here should go away really, diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 98664db..0ceed21 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -820,6 +820,7 @@ asmlinkage long sys_fanotify_init(unsigned int flags, unsigned int event_f_flags asmlinkage long sys_fanotify_mark(int fanotify_fd, unsigned int flags, u64 mask, int fd, const char __user *pathname); +asmlinkage long sys_syncfs(int fd); int kernel_execve(const char *filename, const char *const argv[], const char *const envp[]); -- 1.7.0 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
