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[vfs] Allow offsets for special files other than regular files. 

Some character and block devices can be seekable. So allow their FD to maintain
file offset.

PiperOrigin-RevId: 327370684
This commit is contained in:
Ayush Ranjan 2020-08-18 21:55:16 -07:00 committed by gVisor bot
parent e5f05d9bf4
commit 35dc7fe7e7
1 changed files with 22 additions and 13 deletions
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35
pkg/sentry/fsimpl/gofer/special_file.go
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@ -39,8 +39,14 @@ type specialFileFD struct {
// handle is used for file I/O. handle is immutable.
handle handle
// isRegularFile is true if this FD represents a regular file which is only
// possible when filesystemOptions.regularFilesUseSpecialFileFD is in
// effect. isRegularFile is immutable.
isRegularFile bool
// seekable is true if this file description represents a file for which
// file offset is significant, i.e. a regular file. seekable is immutable.
// file offset is significant, i.e. a regular file, character device or
// block device. seekable is immutable.
seekable bool
// haveQueue is true if this file description represents a file for which
@ -55,12 +61,13 @@ type specialFileFD struct {
func newSpecialFileFD(h handle, mnt *vfs.Mount, d *dentry, locks *vfs.FileLocks, flags uint32) (*specialFileFD, error) {
ftype := d.fileType()
seekable := ftype == linux.S_IFREG
seekable := ftype == linux.S_IFREG || ftype == linux.S_IFCHR || ftype == linux.S_IFBLK
haveQueue := (ftype == linux.S_IFIFO || ftype == linux.S_IFSOCK) && h.fd >= 0
fd := &specialFileFD{
handle: h,
seekable: seekable,
haveQueue: haveQueue,
handle: h,
isRegularFile: ftype == linux.S_IFREG,
seekable: seekable,
haveQueue: haveQueue,
}
fd.LockFD.Init(locks)
if haveQueue {
@ -200,13 +207,13 @@ func (fd *specialFileFD) pwrite(ctx context.Context, src usermem.IOSequence, off
// If the regular file fd was opened with O_APPEND, make sure the file size
// is updated. There is a possible race here if size is modified externally
// after metadata cache is updated.
if fd.seekable && fd.vfsfd.StatusFlags()&linux.O_APPEND != 0 && !d.cachedMetadataAuthoritative() {
if fd.isRegularFile && fd.vfsfd.StatusFlags()&linux.O_APPEND != 0 && !d.cachedMetadataAuthoritative() {
if err := d.updateFromGetattr(ctx); err != nil {
return 0, offset, err
}
}
if fd.seekable {
if fd.isRegularFile {
// We need to hold the metadataMu *while* writing to a regular file.
d.metadataMu.Lock()
defer d.metadataMu.Unlock()
@ -236,18 +243,20 @@ func (fd *specialFileFD) pwrite(ctx context.Context, src usermem.IOSequence, off
if err == syserror.EAGAIN {
err = syserror.ErrWouldBlock
}
finalOff = offset
// Update offset if the offset is valid.
if offset >= 0 {
offset += int64(n)
}
// Update file size for regular files.
if fd.seekable {
finalOff += int64(n)
if fd.isRegularFile {
// d.metadataMu is already locked at this point.
if uint64(finalOff) > d.size {
if uint64(offset) > d.size {
d.dataMu.Lock()
defer d.dataMu.Unlock()
atomic.StoreUint64(&d.size, uint64(finalOff))
atomic.StoreUint64(&d.size, uint64(offset))
}
}
return int64(n), finalOff, err
return int64(n), offset, err
}
// Write implements vfs.FileDescriptionImpl.Write.