linux-ext4 - File name is not persisted if opened with O_SYNC and O

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Message-ID: <4b207a36-5789-41d2-ac17-df86d4cde6da@gmail.com>
Date: Thu, 12 Feb 2026 14:51:47 +0300
From: Vyacheslav Kovalevsky <slava.kovalevskiy.2014@...il.com>
To: viro@...iv.linux.org.uk, brauner@...nel.org
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: File name is not persisted if opened with O_SYNC and O_TRUNC flags

Detailed description
====================

Hello, there seems to be an issue with O_SYNC flag when used together 
with O_TRUNC on various file systems.
Opening a file with O_SYNC (or using fsync(fd)) should persist directory 
entry.
However, if O_SYNC is used together with O_TRUNC the file will be 
missing if system crashes.
According to POSIX this is OK, but most file systems provide stronger 
guarantees (would be actually nice to have a more recent documentation 
on this behavior).
This happens on Btrfs, ext4, XFS, F2FS and likely other file systems.

System info
===========

Linux version 6.19-rc7, also tested on 6.17

How to reproduce
================

```
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
   int status;

   status = creat("file", S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
   printf("CREAT: %d\n", status);
   close(status);

   status = open("file", O_RDWR | O_TRUNC | O_SYNC);
   printf("OPEN: %d\n", status);
}
// after the crash `file` is missing
```

Steps:
1. Create and mount new file system in default configuration.
2. Change directory to root of the file system and run the compiled test.
3. Cause hard system crash (e.g. QEMU `system_reset` command).
4. Remount file system after crash.
5. Observe that file is missing.