Skip to content

Commit

Permalink
wasi: adds platform.Dirent in preparation of inode fetching (#1154)
Browse files Browse the repository at this point in the history 
wasi_snapshot_preview1 recently requires fd_readdir to return actual
inode values. On zero, wasi-libc will call fdstat to retrieve them.

This introduces our own `platform.Dirent` type and `Readdir` function
which a later change will allow fetching of inodes.

See WebAssembly/wasi-libc#345

Signed-off-by: Adrian Cole <adrian@tetrate.io>
  • Loading branch information
@codefromthecrypt
codefromthecrypt authored Feb 23, 2023
1 parent 3a06ae3 commit bb002c8
Show file tree
Hide file tree
Showing 7 changed files with 270 additions and 155 deletions.
83 changes: 48 additions & 35 deletions imports/wasi_snapshot_preview1/fs.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -813,7 +813,7 @@ func fdReaddirFn(_ context.Context, mod api.Module, params []uint64) Errno {
if err != nil {
return ToErrno(err)
}
rd, dir = f.File.(fs.ReadDirFile), f.ReadDir
rd, dir = f.File, f.ReadDir
}

// First, determine the maximum directory entries that can be encoded as
Expand All @@ -831,26 +831,26 @@ func fdReaddirFn(_ context.Context, mod api.Module, params []uint64) Errno {

// The host keeps state for any unread entries from the prior call because
// we cannot seek to a previous directory position. Collect these entries.
entries, errno := lastDirEntries(dir, cookie)
dirents, errno := lastDirents(dir, cookie)
if errno != ErrnoSuccess {
return errno
}

// Add entries for dot and dot-dot as wasi-testsuite requires them.
if cookie == 0 && entries == nil {
if cookie == 0 && dirents == nil {
var err error
if f, ok := fsc.LookupFile(fd); !ok {
return ErrnoBadf
} else if entries, err = sys.DotEntries(f.File); err != nil {
} else if dirents, err = dotDirents(f.File); err != nil {
return ToErrno(err)
}
dir.Entries = entries
dir.Dirents = dirents
dir.CountRead = 2 // . and ..
}

// Check if we have maxDirEntries, and read more from the FS as needed.
if entryCount := len(entries); entryCount < maxDirEntries {
l, err := rd.ReadDir(maxDirEntries - entryCount)
if entryCount := len(dirents); entryCount < maxDirEntries {
l, err := platform.Readdir(rd, maxDirEntries-entryCount)
if err == io.EOF { // EOF is not an error
} else if err != nil {
if errno = ToErrno(err); errno == ErrnoNoent {
Expand All @@ -864,15 +864,15 @@ func fdReaddirFn(_ context.Context, mod api.Module, params []uint64) Errno {
}
} else {
dir.CountRead += uint64(len(l))
entries = append(entries, l...)
dirents = append(dirents, l...)
// Replace the cache with up to maxDirEntries, starting at cookie.
dir.Entries = entries
dir.Dirents = dirents
}
}

// Determine how many dirents we can write, excluding a potentially
// truncated entry.
bufused, direntCount, writeTruncatedEntry := maxDirents(entries, bufLen)
bufused, direntCount, writeTruncatedEntry := maxDirents(dirents, bufLen)

// Now, write entries to the underlying buffer.
if bufused > 0 {
Expand All @@ -883,12 +883,12 @@ func fdReaddirFn(_ context.Context, mod api.Module, params []uint64) Errno {
// ^^ yes this can overflow to negative, which means our implementation
// doesn't support writing greater than max int64 entries.

dirents, ok := mem.Read(buf, bufused)
buf, ok := mem.Read(buf, bufused)
if !ok {
return ErrnoFault
}

writeDirents(entries, direntCount, writeTruncatedEntry, dirents, d_next)
writeDirents(dirents, direntCount, writeTruncatedEntry, buf, d_next)
}

if !mem.WriteUint32Le(resultBufused, bufused) {
Expand All @@ -897,16 +897,29 @@ func fdReaddirFn(_ context.Context, mod api.Module, params []uint64) Errno {
return ErrnoSuccess
}

// dotDirents returns "." and "..", where "." has a real stat because
// wasi-testsuite does inode validation.
func dotDirents(f fs.File) ([]*platform.Dirent, error) {
var st platform.Stat_t
if err := platform.StatFile(f, &st); err != nil {
return nil, err
}
return []*platform.Dirent{
{Name: ".", Ino: st.Ino, Type: fs.ModeDir},
{Name: "..", Type: fs.ModeDir},
}, nil
}

const largestDirent = int64(math.MaxUint32 - DirentSize)

// lastDirEntries is broken out from fdReaddirFn for testability.
func lastDirEntries(dir *sys.ReadDir, cookie int64) (entries []fs.DirEntry, errno Errno) {
// lastDirents is broken out from fdReaddirFn for testability.
func lastDirents(dir *sys.ReadDir, cookie int64) (dirents []*platform.Dirent, errno Errno) {
if cookie < 0 {
errno = ErrnoInval // invalid as we will never send a negative cookie.
return
}

entryCount := int64(len(dir.Entries))
entryCount := int64(len(dir.Dirents))
if entryCount == 0 { // there was no prior call
if cookie != 0 {
errno = ErrnoInval // invalid as we haven't sent that cookie
Expand All @@ -924,12 +937,12 @@ func lastDirEntries(dir *sys.ReadDir, cookie int64) (entries []fs.DirEntry, errn
case cookiePos > entryCount:
errno = ErrnoInval // invalid as we read that far, yet.
case cookiePos > 0: // truncate so to avoid large lists.
entries = dir.Entries[cookiePos:]
dirents = dir.Dirents[cookiePos:]
default:
entries = dir.Entries
dirents = dir.Dirents
}
if len(entries) == 0 {
entries = nil
if len(dirents) == 0 {
dirents = nil
}
return
}
Expand All @@ -943,7 +956,7 @@ func lastDirEntries(dir *sys.ReadDir, cookie int64) (entries []fs.DirEntry, errn
//
// See https://github.com/WebAssembly/WASI/blob/snapshot-01/phases/snapshot/docs.md#fd_readdir
// See https://github.com/WebAssembly/wasi-libc/blob/659ff414560721b1660a19685110e484a081c3d4/libc-bottom-half/cloudlibc/src/libc/dirent/readdir.c#L44
func maxDirents(entries []fs.DirEntry, bufLen uint32) (bufused, direntCount uint32, writeTruncatedEntry bool) {
func maxDirents(entries []*platform.Dirent, bufLen uint32) (bufused, direntCount uint32, writeTruncatedEntry bool) {
lenRemaining := bufLen
for _, e := range entries {
if lenRemaining < DirentSize {
Expand All @@ -957,7 +970,7 @@ func maxDirents(entries []fs.DirEntry, bufLen uint32) (bufused, direntCount uint
}

// use int64 to guard against huge filenames
nameLen := int64(len(e.Name()))
nameLen := int64(len(e.Name))
var entryLen uint32

// Check to see if DirentSize + nameLen overflows, or if it would be
Expand Down Expand Up @@ -1000,21 +1013,21 @@ func maxDirents(entries []fs.DirEntry, bufLen uint32) (bufused, direntCount uint
// based on maxDirents. truncatedEntryLen means write one past entryCount,
// without its name. See maxDirents for why
func writeDirents(
entries []fs.DirEntry,
entryCount uint32,
dirents []*platform.Dirent,
direntCount uint32,
writeTruncatedEntry bool,
dirents []byte,
buf []byte,
d_next uint64,
) {
pos, i := uint32(0), uint32(0)
for ; i < entryCount; i++ {
e := entries[i]
nameLen := uint32(len(e.Name()))
for ; i < direntCount; i++ {
e := dirents[i]
nameLen := uint32(len(e.Name))

writeDirent(dirents[pos:], d_next, nameLen, e.IsDir())
writeDirent(buf[pos:], d_next, nameLen, e.IsDir())
pos += DirentSize

copy(dirents[pos:], e.Name())
copy(buf[pos:], e.Name)
pos += nameLen
d_next++
}
Expand All @@ -1025,11 +1038,11 @@ func writeDirents(

// Write a dirent without its name
dirent := make([]byte, DirentSize)
e := entries[i]
writeDirent(dirent, d_next, uint32(len(e.Name())), e.IsDir())
e := dirents[i]
writeDirent(dirent, d_next, uint32(len(e.Name)), e.IsDir())

// Potentially truncate it
copy(dirents[pos:], dirent)
copy(buf[pos:], dirent)
}

// writeDirent writes DirentSize bytes
Expand All @@ -1046,10 +1059,10 @@ func writeDirent(buf []byte, dNext uint64, dNamlen uint32, dType bool) {
}

// openedDir returns the directory and ErrnoSuccess if the fd points to a readable directory.
func openedDir(fsc *sys.FSContext, fd uint32) (fs.ReadDirFile, *sys.ReadDir, Errno) {
func openedDir(fsc *sys.FSContext, fd uint32) (fs.File, *sys.ReadDir, Errno) {
if f, ok := fsc.LookupFile(fd); !ok {
return nil, nil, ErrnoBadf
} else if d, ok := f.File.(fs.ReadDirFile); !ok {
} else if !f.IsDir() {
// fd_readdir docs don't indicate whether to return ErrnoNotdir or
// ErrnoBadf. It has been noticed that rust will crash on ErrnoNotdir,
// and POSIX C ref seems to not return this, so we don't either.
Expand All @@ -1061,7 +1074,7 @@ func openedDir(fsc *sys.FSContext, fd uint32) (fs.ReadDirFile, *sys.ReadDir, Err
if f.ReadDir == nil {
f.ReadDir = &sys.ReadDir{}
}
return d, f.ReadDir, ErrnoSuccess
return f.File, f.ReadDir, ErrnoSuccess
}
}

Expand Down
Loading

0 comments on commit bb002c8

Please sign in to comment.