diff options
Diffstat (limited to 'pkg/sentry/fs/ext/filesystem.go')
| -rw-r--r-- | pkg/sentry/fs/ext/filesystem.go | 26 |
1 files changed, 10 insertions, 16 deletions
diff --git a/pkg/sentry/fs/ext/filesystem.go b/pkg/sentry/fs/ext/filesystem.go index 32ca11026..12aeb5dac 100644 --- a/pkg/sentry/fs/ext/filesystem.go +++ b/pkg/sentry/fs/ext/filesystem.go @@ -31,22 +31,16 @@ type filesystem struct { vfsfs vfs.Filesystem - // mu serializes changes to the Dentry tree and the usage of the read seeker. - mu sync.Mutex + // mu serializes changes to the Dentry tree. + mu sync.RWMutex - // dev is the ReadSeeker for the underlying fs device. It is protected by mu. - // - // The ext filesystems aim to maximize locality, i.e. place all the data - // blocks of a file close together. On a spinning disk, locality reduces the - // amount of movement of the head hence speeding up IO operations. On an SSD - // there are no moving parts but locality increases the size of each transer - // request. Hence, having mutual exclusion on the read seeker while reading a - // file *should* help in achieving the intended performance gains. - // - // Note: This synchronization was not coupled with the ReadSeeker itself - // because we want to synchronize across read/seek operations for the - // performance gains mentioned above. Helps enforcing one-file-at-a-time IO. - dev io.ReadSeeker + // dev is the io.ReaderAt for the underlying fs device. It does not require + // protection because io.ReaderAt permits concurrent read calls to it. It + // translates to the pread syscall which passes on the read request directly + // to the device driver. Device drivers are intelligent in serving multiple + // concurrent read requests in the optimal order (taking locality into + // consideration). + dev io.ReaderAt // inodeCache maps absolute inode numbers to the corresponding Inode struct. // Inodes should be removed from this once their reference count hits 0. @@ -69,7 +63,7 @@ var _ vfs.FilesystemImpl = (*filesystem)(nil) // getOrCreateInode gets the inode corresponding to the inode number passed in. // It creates a new one with the given inode number if one does not exist. // -// Preconditions: must be holding fs.mu. +// Precondition: must be holding fs.mu. func (fs *filesystem) getOrCreateInode(ctx context.Context, inodeNum uint32) (*inode, error) { if in, ok := fs.inodeCache[inodeNum]; ok { return in, nil |