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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package pipe
import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/syserror"
)
// inodeOperations implements fs.InodeOperations for pipes.
//
// +stateify savable
type inodeOperations struct {
fsutil.InodeGenericChecker `state:"nosave"`
fsutil.InodeNoExtendedAttributes `state:"nosave"`
fsutil.InodeNoopRelease `state:"nosave"`
fsutil.InodeNoopTruncate `state:"nosave"`
fsutil.InodeNoopWriteOut `state:"nosave"`
fsutil.InodeNotDirectory `state:"nosave"`
fsutil.InodeNotMappable `state:"nosave"`
fsutil.InodeNotSocket `state:"nosave"`
fsutil.InodeNotSymlink `state:"nosave"`
// Marking pipe inodes as virtual allows them to be saved and restored
// even if they have been unlinked. We can get away with this because
// their state exists entirely within the sentry.
fsutil.InodeVirtual `state:"nosave"`
fsutil.InodeSimpleAttributes
// mu protects the fields below.
mu sync.Mutex `state:"nosave"`
// p is the underlying Pipe object representing this fifo.
p *Pipe
// Channels for synchronizing the creation of new readers and writers of
// this fifo. See waitFor and newHandleLocked.
//
// These are not saved/restored because all waiters are unblocked on save,
// and either automatically restart (via ERESTARTSYS) or return EINTR on
// resume. On restarts via ERESTARTSYS, the appropriate channel will be
// recreated.
rWakeup chan struct{} `state:"nosave"`
wWakeup chan struct{} `state:"nosave"`
}
var _ fs.InodeOperations = (*inodeOperations)(nil)
// NewInodeOperations returns a new fs.InodeOperations for a given pipe.
func NewInodeOperations(ctx context.Context, perms fs.FilePermissions, p *Pipe) *inodeOperations {
return &inodeOperations{
InodeSimpleAttributes: fsutil.NewInodeSimpleAttributes(ctx, fs.FileOwnerFromContext(ctx), perms, linux.PIPEFS_MAGIC),
p: p,
}
}
// GetFile implements fs.InodeOperations.GetFile. Named pipes have special blocking
// semantics during open:
//
// "Normally, opening the FIFO blocks until the other end is opened also. A
// process can open a FIFO in nonblocking mode. In this case, opening for
// read-only will succeed even if no-one has opened on the write side yet,
// opening for write-only will fail with ENXIO (no such device or address)
// unless the other end has already been opened. Under Linux, opening a FIFO
// for read and write will succeed both in blocking and nonblocking mode. POSIX
// leaves this behavior undefined. This can be used to open a FIFO for writing
// while there are no readers available." - fifo(7)
func (i *inodeOperations) GetFile(ctx context.Context, d *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
i.mu.Lock()
defer i.mu.Unlock()
switch {
case flags.Read && !flags.Write: // O_RDONLY.
r := i.p.Open(ctx, d, flags)
newHandleLocked(&i.rWakeup)
if i.p.isNamed && !flags.NonBlocking && !i.p.HasWriters() {
if !waitFor(&i.mu, &i.wWakeup, ctx) {
r.DecRef(ctx)
return nil, syserror.ErrInterrupted
}
}
// By now, either we're doing a nonblocking open or we have a writer. On
// a nonblocking read-only open, the open succeeds even if no-one has
// opened the write side yet.
return r, nil
case flags.Write && !flags.Read: // O_WRONLY.
w := i.p.Open(ctx, d, flags)
newHandleLocked(&i.wWakeup)
if i.p.isNamed && !i.p.HasReaders() {
// On a nonblocking, write-only open, the open fails with ENXIO if the
// read side isn't open yet.
if flags.NonBlocking {
w.DecRef(ctx)
return nil, syserror.ENXIO
}
if !waitFor(&i.mu, &i.rWakeup, ctx) {
w.DecRef(ctx)
return nil, syserror.ErrInterrupted
}
}
return w, nil
case flags.Read && flags.Write: // O_RDWR.
// Pipes opened for read-write always succeeds without blocking.
rw := i.p.Open(ctx, d, flags)
newHandleLocked(&i.rWakeup)
newHandleLocked(&i.wWakeup)
return rw, nil
default:
return nil, syserror.EINVAL
}
}
func (*inodeOperations) Allocate(_ context.Context, _ *fs.Inode, _, _ int64) error {
return syserror.EPIPE
}
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