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Clean up hostfs TODOs.

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This CL does a handful of things:
- Support O_DSYNC, O_SYNC
- Support O_APPEND and document an unavoidable race condition
- Ignore O_DIRECT; we probably don't want to allow applications to set O_DIRECT
  on the host fd itself.
- Leave a TODO for supporting O_NONBLOCK, which is a simple fix once RWF_NOWAIT
  is supported.
- Get rid of caching TODO; force_page_cache is not configurable for host fs in
  vfs1 or vfs2 after whitelist fs was removed.
- For the remaining TODOs, link to more specific bugs.

Fixes #1672.

PiperOrigin-RevId: 317985269
This commit is contained in:
Dean Deng
2020-06-23 19:24:43 -07:00
committed by gVisor bot
parent 2141013dce
commit 2189e0a660
1 changed files with 32 additions and 15 deletions
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pkg/sentry/fsimpl/host/host.go
+32 -15
View File
@@ -459,8 +459,9 @@ func (i *inode) open(ctx context.Context, d *vfs.Dentry, mnt *vfs.Mount, flags u
fileType := s.Mode & linux.FileTypeMask
// Constrain flags to a subset we can handle.
// TODO(gvisor.dev/issue/1672): implement behavior corresponding to these allowed flags.
flags &= syscall.O_ACCMODE | syscall.O_DIRECT | syscall.O_NONBLOCK | syscall.O_DSYNC | syscall.O_SYNC | syscall.O_APPEND
//
// TODO(gvisor.dev/issue/2601): Support O_NONBLOCK by adding RWF_NOWAIT to pread/pwrite calls.
flags &= syscall.O_ACCMODE | syscall.O_NONBLOCK | syscall.O_DSYNC | syscall.O_SYNC | syscall.O_APPEND
switch fileType {
case syscall.S_IFSOCK:
@@ -568,7 +569,7 @@ func (f *fileDescription) Read(ctx context.Context, dst usermem.IOSequence, opts
}
return n, err
}
// TODO(gvisor.dev/issue/1672): Cache pages, when forced to do so.
f.offsetMu.Lock()
n, err := readFromHostFD(ctx, i.hostFD, dst, f.offset, opts.Flags)
f.offset += n
@@ -577,7 +578,7 @@ func (f *fileDescription) Read(ctx context.Context, dst usermem.IOSequence, opts
}
func readFromHostFD(ctx context.Context, hostFD int, dst usermem.IOSequence, offset int64, flags uint32) (int64, error) {
// TODO(gvisor.dev/issue/1672): Support select preadv2 flags.
// TODO(gvisor.dev/issue/2601): Support select preadv2 flags.
if flags != 0 {
return 0, syserror.EOPNOTSUPP
}
@@ -589,41 +590,58 @@ func readFromHostFD(ctx context.Context, hostFD int, dst usermem.IOSequence, off
// PWrite implements FileDescriptionImpl.
func (f *fileDescription) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
i := f.inode
if !i.seekable {
if !f.inode.seekable {
return 0, syserror.ESPIPE
}
return writeToHostFD(ctx, i.hostFD, src, offset, opts.Flags)
return f.writeToHostFD(ctx, src, offset, opts.Flags)
}
// Write implements FileDescriptionImpl.
func (f *fileDescription) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
i := f.inode
if !i.seekable {
n, err := writeToHostFD(ctx, i.hostFD, src, -1, opts.Flags)
n, err := f.writeToHostFD(ctx, src, -1, opts.Flags)
if isBlockError(err) {
err = syserror.ErrWouldBlock
}
return n, err
}
// TODO(gvisor.dev/issue/1672): Cache pages, when forced to do so.
// TODO(gvisor.dev/issue/1672): Write to end of file and update offset if O_APPEND is set on this file.
f.offsetMu.Lock()
n, err := writeToHostFD(ctx, i.hostFD, src, f.offset, opts.Flags)
// NOTE(gvisor.dev/issue/2983): O_APPEND may cause memory corruption if
// another process modifies the host file between retrieving the file size
// and writing to the host fd. This is an unavoidable race condition because
// we cannot enforce synchronization on the host.
if f.vfsfd.StatusFlags()&linux.O_APPEND != 0 {
var s syscall.Stat_t
if err := syscall.Fstat(i.hostFD, &s); err != nil {
f.offsetMu.Unlock()
return 0, err
}
f.offset = s.Size
}
n, err := f.writeToHostFD(ctx, src, f.offset, opts.Flags)
f.offset += n
f.offsetMu.Unlock()
return n, err
}
func writeToHostFD(ctx context.Context, hostFD int, src usermem.IOSequence, offset int64, flags uint32) (int64, error) {
// TODO(gvisor.dev/issue/1672): Support select pwritev2 flags.
func (f *fileDescription) writeToHostFD(ctx context.Context, src usermem.IOSequence, offset int64, flags uint32) (int64, error) {
hostFD := f.inode.hostFD
// TODO(gvisor.dev/issue/2601): Support select pwritev2 flags.
if flags != 0 {
return 0, syserror.EOPNOTSUPP
}
writer := hostfd.GetReadWriterAt(int32(hostFD), offset, flags)
n, err := src.CopyInTo(ctx, writer)
hostfd.PutReadWriterAt(writer)
// NOTE(gvisor.dev/issue/2979): We always sync everything, even for O_DSYNC.
if n > 0 && f.vfsfd.StatusFlags()&(linux.O_DSYNC|linux.O_SYNC) != 0 {
if syncErr := unix.Fsync(hostFD); syncErr != nil {
return int64(n), syncErr
}
}
return int64(n), err
}
@@ -694,8 +712,7 @@ func (f *fileDescription) Seek(_ context.Context, offset int64, whence int32) (i
// Sync implements FileDescriptionImpl.
func (f *fileDescription) Sync(context.Context) error {
// TODO(gvisor.dev/issue/1672): Currently we do not support the SyncData
// optimization, so we always sync everything.
// TODO(gvisor.dev/issue/1897): Currently, we always sync everything.
return unix.Fsync(f.inode.hostFD)
}