Implement sync_file_range()
sync_file_range - sync a file segment with disk In Linux, sync_file_range() accepts three flags: SYNC_FILE_RANGE_WAIT_BEFORE Wait upon write-out of all pages in the specified range that have already been submitted to the device driver for write-out before performing any write. SYNC_FILE_RANGE_WRITE Initiate write-out of all dirty pages in the specified range which are not presently submitted write-out. Note that even this may block if you attempt to write more than request queue size. SYNC_FILE_RANGE_WAIT_AFTER Wait upon write-out of all pages in the range after performing any write. In this implementation: SYNC_FILE_RANGE_WAIT_BEFORE without SYNC_FILE_RANGE_WAIT_AFTER isn't supported right now. SYNC_FILE_RANGE_WRITE is skipped. It should initiate write-out of all dirty pages, but it doesn't wait, so it should be safe to do nothing while nobody uses SYNC_FILE_RANGE_WAIT_BEFORE. SYNC_FILE_RANGE_WAIT_AFTER is equal to fdatasync(). In Linux, sync_file_range() doesn't writes out the file's meta-data, but fdatasync() does if a file size is changed. PiperOrigin-RevId: 220730840 Change-Id: Iae5dfb23c2c916967d67cf1a1ad32f25eb3f6286
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@ -73,3 +73,10 @@ type Statfs struct {
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// Spare is unused.
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Spare [4]uint64
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}
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// Sync_file_range flags, from include/uapi/linux/fs.h
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const (
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SYNC_FILE_RANGE_WAIT_BEFORE = 1
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SYNC_FILE_RANGE_WRITE = 2
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SYNC_FILE_RANGE_WAIT_AFTER = 4
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)
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@ -325,7 +325,7 @@ var AMD64 = &kernel.SyscallTable{
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274: syscalls.Error(syscall.ENOSYS), // GetRobustList, obsolete
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// 275: Splice, TODO
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// 276: Tee, TODO
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// 277: SyncFileRange, TODO
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277: SyncFileRange,
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// 278: Vmsplice, TODO
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279: syscalls.CapError(linux.CAP_SYS_NICE), // MovePages, requires cap_sys_nice (mostly)
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280: Utimensat,
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@ -15,6 +15,7 @@
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package linux
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import (
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"gvisor.googlesource.com/gvisor/pkg/abi/linux"
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"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
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"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
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"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
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@ -73,3 +74,65 @@ func Fdatasync(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sys
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err := file.Fsync(t, 0, fs.FileMaxOffset, fs.SyncData)
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return 0, nil, syserror.ConvertIntr(err, kernel.ERESTARTSYS)
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}
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// SyncFileRange implements linux syscall sync_file_rage(2)
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func SyncFileRange(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
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var err error
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offset := args[1].Int64()
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nbytes := args[2].Int64()
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uflags := args[3].Uint()
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if offset < 0 || offset+nbytes < offset {
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return 0, nil, syserror.EINVAL
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}
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if uflags&^(linux.SYNC_FILE_RANGE_WAIT_BEFORE|
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linux.SYNC_FILE_RANGE_WRITE|
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linux.SYNC_FILE_RANGE_WAIT_AFTER) != 0 {
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return 0, nil, syserror.EINVAL
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}
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if nbytes == 0 {
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nbytes = fs.FileMaxOffset
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}
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fd := kdefs.FD(args[0].Int())
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file := t.FDMap().GetFile(fd)
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if file == nil {
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return 0, nil, syserror.EBADF
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}
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defer file.DecRef()
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// SYNC_FILE_RANGE_WAIT_BEFORE waits upon write-out of all pages in the
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// specified range that have already been submitted to the device
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// driver for write-out before performing any write.
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if uflags&linux.SYNC_FILE_RANGE_WAIT_BEFORE != 0 &&
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uflags&linux.SYNC_FILE_RANGE_WAIT_AFTER == 0 {
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t.Kernel().EmitUnimplementedEvent(t)
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return 0, nil, syserror.ENOSYS
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}
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// SYNC_FILE_RANGE_WRITE initiates write-out of all dirty pages in the
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// specified range which are not presently submitted write-out.
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//
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// It looks impossible to implement this functionality without a
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// massive rework of the vfs subsystem. file.Fsync() take a file lock
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// for the entire operation, so even if it is running in a go routing,
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// it blocks other file operations instead of flushing data in the
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// background.
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//
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// It should be safe to skipped this flag while nobody uses
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// SYNC_FILE_RANGE_WAIT_BEFORE.
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// SYNC_FILE_RANGE_WAIT_AFTER waits upon write-out of all pages in the
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// range after performing any write.
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//
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// In Linux, sync_file_range() doesn't writes out the file's
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// meta-data, but fdatasync() does if a file size is changed.
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if uflags&linux.SYNC_FILE_RANGE_WAIT_AFTER != 0 {
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err = file.Fsync(t, offset, fs.FileMaxOffset, fs.SyncData)
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}
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return 0, nil, syserror.ConvertIntr(err, kernel.ERESTARTSYS)
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}
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