From ed5f8487b15f1d9cd83b4b0a4220271b6c5f189e Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Sun, 1 Feb 2026 20:05:13 +0100
Subject: syscallcompat: DetectQuirks: suppress Btrfs message when -noprealloc
 has been passed

Reported by @Tunoac, https://github.com/rfjakob/gocryptfs/issues/395#issuecomment-3828507487
---
 internal/fusefrontend/file.go          | 4 ++--
 internal/fusefrontend/root_node.go     | 4 ++++
 internal/syscallcompat/quirks.go       | 7 ++++---
 internal/syscallcompat/quirks_linux.go | 4 ++--
 4 files changed, 12 insertions(+), 7 deletions(-)

(limited to 'internal')

diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
index afee158..64c6ca0 100644
--- a/internal/fusefrontend/file.go
+++ b/internal/fusefrontend/file.go
@@ -115,7 +115,7 @@ func (f *File) createHeader() (fileID []byte, err error) {
 	h := contentenc.RandomHeader()
 	buf := h.Pack()
 	// Prevent partially written (=corrupt) header by preallocating the space beforehand
-	if !f.rootNode.args.NoPrealloc && f.rootNode.quirks&syscallcompat.QuirkBrokenFalloc == 0 {
+	if !f.rootNode.args.NoPrealloc && f.rootNode.quirks&syscallcompat.QuirkBtrfsBrokenFalloc == 0 {
 		err = syscallcompat.EnospcPrealloc(f.intFd(), 0, contentenc.HeaderLen)
 		if err != nil {
 			if !syscallcompat.IsENOSPC(err) {
@@ -315,7 +315,7 @@ func (f *File) doWrite(data []byte, off int64) (uint32, syscall.Errno) {
 	if cOff > math.MaxInt64 {
 		return 0, syscall.EFBIG
 	}
-	if !f.rootNode.args.NoPrealloc && f.rootNode.quirks&syscallcompat.QuirkBrokenFalloc == 0 {
+	if !f.rootNode.args.NoPrealloc && f.rootNode.quirks&syscallcompat.QuirkBtrfsBrokenFalloc == 0 {
 		err = syscallcompat.EnospcPrealloc(f.intFd(), int64(cOff), int64(len(ciphertext)))
 		if err != nil {
 			if !syscallcompat.IsENOSPC(err) {
diff --git a/internal/fusefrontend/root_node.go b/internal/fusefrontend/root_node.go
index 8464c5f..489e3c6 100644
--- a/internal/fusefrontend/root_node.go
+++ b/internal/fusefrontend/root_node.go
@@ -91,6 +91,10 @@ func NewRootNode(args Args, c *contentenc.ContentEnc, n *nametransform.NameTrans
 		dirCache:      dirCache{ivLen: ivLen},
 		quirks:        syscallcompat.DetectQuirks(args.Cipherdir),
 	}
+	// Suppress the message if the user has already specified -noprealloc
+	if rn.quirks&syscallcompat.QuirkBtrfsBrokenFalloc != 0 && !args.NoPrealloc {
+		syscallcompat.LogQuirk("Btrfs detected, forcing -noprealloc. See https://github.com/rfjakob/gocryptfs/issues/395 for why.")
+	}
 	if statErr == nil {
 		rn.inoMap.TranslateStat(&st)
 		rn.rootIno = st.Ino
diff --git a/internal/syscallcompat/quirks.go b/internal/syscallcompat/quirks.go
index e30d605..36bcb9f 100644
--- a/internal/syscallcompat/quirks.go
+++ b/internal/syscallcompat/quirks.go
@@ -5,16 +5,17 @@ import (
 )
 
 const (
-	// QuirkBrokenFalloc means the falloc is broken.
+	// QuirkBtrfsBrokenFalloc means the falloc is broken.
 	// Preallocation on Btrfs is broken ( https://github.com/rfjakob/gocryptfs/issues/395 )
 	// and slow ( https://github.com/rfjakob/gocryptfs/issues/63 ).
-	QuirkBrokenFalloc = uint64(1 << iota)
+	QuirkBtrfsBrokenFalloc = uint64(1 << iota)
 	// QuirkDuplicateIno1 means that we have duplicate inode numbers.
 	// On MacOS ExFAT, all empty files share inode number 1:
 	// https://github.com/rfjakob/gocryptfs/issues/585
 	QuirkDuplicateIno1
 )
 
-func logQuirk(s string) {
+// LogQuirk prints a yellow message about a detected quirk.
+func LogQuirk(s string) {
 	tlog.Info.Println(tlog.ColorYellow + "DetectQuirks: " + s + tlog.ColorReset)
 }
diff --git a/internal/syscallcompat/quirks_linux.go b/internal/syscallcompat/quirks_linux.go
index bcdcf07..87af03d 100644
--- a/internal/syscallcompat/quirks_linux.go
+++ b/internal/syscallcompat/quirks_linux.go
@@ -23,8 +23,8 @@ func DetectQuirks(cipherdir string) (q uint64) {
 	//
 	// Cast to uint32 avoids compile error on arm: "constant 2435016766 overflows int32"
 	if uint32(st.Type) == unix.BTRFS_SUPER_MAGIC {
-		logQuirk("Btrfs detected, forcing -noprealloc. See https://github.com/rfjakob/gocryptfs/issues/395 for why.")
-		q |= QuirkBrokenFalloc
+		// LogQuirk is called in fusefrontend/root_node.go
+		q |= QuirkBtrfsBrokenFalloc
 	}
 
 	return q
-- 
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