os: emulate plan 9 libc in stat
This change is a recreation of the CL written
by Nick Owens on http://golang.org/cl/150730043.
If the stat buffer is too short, the kernel
informs us by putting the 2-byte size in the
buffer, so we read that and try again.
This follows the same algorithm as /sys/src/libc/9sys/dirfstat.c.
Fixes #8781.
Change-Id: I01b4ad3a5e705dd4cab6673c7a119f8bef9bbd7c
Reviewed-on: https://go-review.googlesource.com/3281
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/os/stat_plan9.go b/src/os/stat_plan9.go
index 25c9a8c..5722787 100644
--- a/src/os/stat_plan9.go
+++ b/src/os/stat_plan9.go
@@ -9,6 +9,8 @@
"time"
)
+const _BIT16SZ = 2
+
func sameFile(fs1, fs2 *fileStat) bool {
a := fs1.sys.(*syscall.Dir)
b := fs2.sys.(*syscall.Dir)
@@ -41,16 +43,14 @@
// arg is an open *File or a path string.
func dirstat(arg interface{}) (*syscall.Dir, error) {
var name string
+ var err error
- // This is big enough for most stat messages
- // and rounded to a multiple of 128 bytes.
- size := (syscall.STATFIXLEN + 16*4 + 128) &^ 128
+ size := syscall.STATFIXLEN + 16*4
for i := 0; i < 2; i++ {
- buf := make([]byte, size)
+ buf := make([]byte, _BIT16SZ+size)
var n int
- var err error
switch a := arg.(type) {
case *File:
name = a.name
@@ -61,10 +61,8 @@
default:
panic("phase error in dirstat")
}
- if err != nil {
- return nil, &PathError{"stat", name, err}
- }
- if n < syscall.STATFIXLEN {
+
+ if n < _BIT16SZ {
return nil, &PathError{"stat", name, syscall.ErrShortStat}
}
@@ -73,17 +71,21 @@
// If the stat message is larger than our buffer we will
// go around the loop and allocate one that is big enough.
- if size > n {
- continue
+ if size <= n {
+ d, err := syscall.UnmarshalDir(buf[:n])
+ if err != nil {
+ return nil, &PathError{"stat", name, err}
+ }
+ return d, nil
}
- d, err := syscall.UnmarshalDir(buf[:n])
- if err != nil {
- return nil, &PathError{"stat", name, err}
- }
- return d, nil
}
- return nil, &PathError{"stat", name, syscall.ErrBadStat}
+
+ if err == nil {
+ err = syscall.ErrBadStat
+ }
+
+ return nil, &PathError{"stat", name, err}
}
// Stat returns a FileInfo describing the named file.
