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Detect the need to increase buffer size on TrueNAS SCALE. #73

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Merged
kuba-- merged 1 commit into from
Jul 21, 2024
Merged

Detect the need to increase buffer size on TrueNAS SCALE. #73

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9 changes: 5 additions & 4 deletions xattr.go
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Original file line number Diff line number Diff line change
Expand Up @@ -87,8 +87,8 @@ func get(path string, name string, getxattrFunc getxattrFunc) ([]byte, error) {
initialBufSize = 1024

// The theoretical maximum xattr value size on MacOS is 64 MB. On Linux it's
// much smaller at 64 KB. Unless the kernel is evil or buggy, we should never
// hit the limit.
// much smaller: documented at 64 KB. However, at least on TrueNAS SCALE, a
// Debian-based Linux distro, it can be larger.
maxBufSize = 64 * 1024 * 1024

// Function name as reported in error messages
Expand All @@ -102,14 +102,15 @@ func get(path string, name string, getxattrFunc getxattrFunc) ([]byte, error) {

// If the buffer was too small to fit the value, Linux and MacOS react
// differently:
// Linux: returns an ERANGE error and "-1" bytes.
// Linux: returns an ERANGE error and "-1" bytes. However, the TrueNAS
// SCALE distro sometimes returns E2BIG.
// MacOS: truncates the value and returns "size" bytes. If the value
// happens to be exactly as big as the buffer, we cannot know if it was
// truncated, and we retry with a bigger buffer. Contrary to documentation,
// MacOS never seems to return ERANGE!
// To keep the code simple, we always check both conditions, and sometimes
// double the buffer size without it being strictly necessary.
if err == syscall.ERANGE || read == size {
if err == syscall.ERANGE || err == syscall.E2BIG || read == size {
// The buffer was too small. Try again.
size <<= 1
if size >= maxBufSize {
Expand Down