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Minor fixes in fd_table.

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- Fixed up some documentation.
- Got rid of some redundant FDTable.get() calls from FDTable.Remove() and
  FDTable.RemoveNextInRange().
- Consistently handled the result of FDTable.set().
- Added file != nil precondition to NewFDAt().
- Only call fdBitmap.Add() and fdBitmap.Remove() when necessary.

PiperOrigin-RevId: 583096816
This commit is contained in:
Ayush Ranjan
2023-11-16 10:51:24 -08:00
committed by gVisor bot
parent 201a046299
commit f154acfb7b
2 changed files with 47 additions and 53 deletions
Download Patch File Download Diff File Expand all files Collapse all files
pkg/sentry/kernel/fd_table.go
+42 -48
View File
@@ -110,7 +110,7 @@ func (f *FDTable) loadDescriptorTable(m map[int32]descriptor) {
panic(fmt.Sprintf("FD is not supposed to be negative. FD: %d", fd))
}
if file := f.set(fd, d.file, d.flags); file != nil {
if df := f.set(fd, d.file, d.flags); df != nil {
panic("file set")
}
f.fdBitmap.Add(uint32(fd))
@@ -271,7 +271,9 @@ func (f *FDTable) NewFDs(ctx context.Context, minFD int32, files []*vfs.FileDesc
break
}
f.fdBitmap.Add(fd)
f.set(int32(fd), files[len(fds)], flags)
if df := f.set(int32(fd), files[len(fds)], flags); df != nil {
panic("file set")
}
fds = append(fds, int32(fd))
minFD = int32(fd)
}
@@ -279,7 +281,7 @@ func (f *FDTable) NewFDs(ctx context.Context, minFD int32, files []*vfs.FileDesc
// Failure? Unwind existing FDs.
if len(fds) < len(files) {
for _, i := range fds {
f.set(i, nil, FDFlags{})
_ = f.set(i, nil, FDFlags{})
f.fdBitmap.Remove(uint32(i))
}
f.mu.Unlock()
@@ -309,47 +311,40 @@ func (f *FDTable) NewFD(ctx context.Context, minFD int32, file *vfs.FileDescript
return fileSlice[0], nil
}
// NewFDAt sets the file reference for the given FD. If there is an active
// reference for that FD, the ref count for that existing reference is
// decremented.
// NewFDAt sets the file reference for the given FD. If there is an existing
// file description for that FD, the table reference for that file description
// is dropped.
//
// Precondition: file != nil.
func (f *FDTable) NewFDAt(ctx context.Context, fd int32, file *vfs.FileDescription, flags FDFlags) error {
df, err := f.newFDAt(ctx, fd, file, flags)
if err != nil {
return err
}
if df != nil {
f.drop(ctx, df)
}
return nil
}
func (f *FDTable) newFDAt(ctx context.Context, fd int32, file *vfs.FileDescription, flags FDFlags) (*vfs.FileDescription, error) {
if fd < 0 {
// Don't accept negative FDs.
return nil, unix.EBADF
return unix.EBADF
}
if fd >= f.k.MaxFDLimit.Load() {
return nil, unix.EMFILE
return unix.EMFILE
}
// Check the limit for the provided file.
if limitSet := limits.FromContext(ctx); limitSet != nil {
if lim := limitSet.Get(limits.NumberOfFiles); lim.Cur != limits.Infinity && uint64(fd) >= lim.Cur {
return nil, unix.EMFILE
return unix.EMFILE
}
}
// Install the entry.
f.mu.Lock()
defer f.mu.Unlock()
df := f.set(fd, file, flags)
// Add fd to fdBitmap.
if file != nil {
if df == nil {
f.fdBitmap.Add(uint32(fd))
}
f.mu.Unlock()
return df, nil
if df != nil {
f.drop(ctx, df)
}
return nil
}
// SetFlags sets the flags for the given file descriptor.
@@ -371,7 +366,9 @@ func (f *FDTable) SetFlags(ctx context.Context, fd int32, flags FDFlags) error {
}
// Update the flags.
f.set(fd, file, flags)
if df := f.set(fd, file, flags); df != nil {
panic("file changed")
}
return nil
}
@@ -388,7 +385,9 @@ func (f *FDTable) SetFlagsForRange(ctx context.Context, startFd int32, endFd int
for fd, err := f.fdBitmap.FirstOne(uint32(startFd)); err == nil && fd <= uint32(endFd); fd, err = f.fdBitmap.FirstOne(fd + 1) {
fdI32 := int32(fd)
file, _, _ := f.get(fdI32)
f.set(fdI32, file, flags)
if df := f.set(fdI32, file, flags); df != nil {
panic("file changed")
}
}
return nil
@@ -460,8 +459,7 @@ func (f *FDTable) Fork(ctx context.Context, maxFd int32) *FDTable {
return clone
}
// Remove removes an FD from and returns a tuple where one of the files is non-nil
// iff successful.
// Remove removes an FD from f. It returns the removed file description.
//
// N.B. Callers are required to use DecRef on the returned file when they are done.
func (f *FDTable) Remove(ctx context.Context, fd int32) *vfs.FileDescription {
@@ -470,19 +468,18 @@ func (f *FDTable) Remove(ctx context.Context, fd int32) *vfs.FileDescription {
}
f.mu.Lock()
file, _, _ := f.get(fd)
if file != nil {
df := f.set(fd, nil, FDFlags{}) // Zap entry.
if df != nil {
// Add reference for caller.
file.IncRef()
file = f.set(fd, nil, FDFlags{}) // Zap entry.
df.IncRef()
f.fdBitmap.Remove(uint32(fd))
}
f.mu.Unlock()
if file != nil {
f.drop(ctx, file)
if df != nil {
f.drop(ctx, df)
}
return file
return df
}
// RemoveIf removes all FDs where cond is true.
@@ -492,9 +489,9 @@ func (f *FDTable) RemoveIf(ctx context.Context, cond func(*vfs.FileDescription,
f.mu.Lock()
f.forEach(ctx, func(fd int32, file *vfs.FileDescription, flags FDFlags) {
if cond(file, flags) {
df := f.set(fd, nil, FDFlags{}) // Clear from table.
f.fdBitmap.Remove(uint32(fd))
if df != nil {
// Clear from table.
if df := f.set(fd, nil, FDFlags{}); df != nil {
f.fdBitmap.Remove(uint32(fd))
files = append(files, df)
}
}
@@ -507,7 +504,7 @@ func (f *FDTable) RemoveIf(ctx context.Context, cond func(*vfs.FileDescription,
}
// RemoveNextInRange removes the next FD that falls within the given range,
// and returns a tuple where one of the files is non-nil iff successful.
// and returns the FD number and FileDescription of the removed FD.
//
// N.B. Callers are required to use DecRef on the returned file when they are done.
func (f *FDTable) RemoveNextInRange(ctx context.Context, startFd int32, endFd int32) (int32, *vfs.FileDescription) {
@@ -523,21 +520,18 @@ func (f *FDTable) RemoveNextInRange(ctx context.Context, startFd int32, endFd in
f.mu.Unlock()
return MaxFdLimit, nil
}
file, _, _ := f.get(fd)
if file != nil {
df := f.set(fd, nil, FDFlags{}) // Zap entry.
if df != nil {
// Add reference for caller.
file.IncRef()
file = f.set(fd, nil, FDFlags{}) // Zap entry.
df.IncRef()
f.fdBitmap.Remove(uint32(fd))
}
f.mu.Unlock()
if file != nil {
f.drop(ctx, file)
if df != nil {
f.drop(ctx, df)
}
return fd, file
return fd, df
}
// GetLastFd returns the last set FD in the FDTable bitmap.
pkg/sentry/kernel/fd_table_unsafe.go
+5 -5
View File
@@ -86,11 +86,11 @@ func (f *FDTable) CurrentMaxFDs() int {
return len(slice) * fdsPerBucket
}
// set sets the file description referred to by fd to file. If
// file is non-nil, it takes a reference on them. If setAll replaces
// an existing file description, it returns it with the FDTable's reference
// transferred to the caller, which must call f.drop on the returned
// file after unlocking f.mu.
// set sets the file description referred to by fd to file. If file is non-nil,
// f takes a reference on it. If file is nil, the file entry at fd is cleared.
// If set replaces an existing file description that is different from `file`,
// it returns it with the FDTable's reference transferred to the caller, which
// must call f.drop on the returned file after unlocking f.mu.
//
// Precondition: mu must be held.
func (f *FDTable) set(fd int32, file *vfs.FileDescription, flags FDFlags) *vfs.FileDescription {