From: bugzilla-daemon@kernel.org
To: linux-ext4@vger.kernel.org
Subject: [Bug 218820] New: The empty file occupies incorrect blocks
Date: Wed, 08 May 2024 13:33:56 +0000 [thread overview]
Message-ID: <bug-218820-13602@https.bugzilla.kernel.org/> (raw)
https://bugzilla.kernel.org/show_bug.cgi?id=218820
Bug ID: 218820
Summary: The empty file occupies incorrect blocks
Product: File System
Version: 2.5
Hardware: All
OS: Linux
Status: NEW
Severity: normal
Priority: P3
Component: ext4
Assignee: fs_ext4@kernel-bugs.osdl.org
Reporter: zhangchi_seg@smail.nju.edu.cn
Regression: No
Created attachment 306275
--> https://bugzilla.kernel.org/attachment.cgi?id=306275&action=edit
reproduce.c
Hi,
I mounted an ext4 image, created a file, and wrote to it, but the blocks
occupied by this file were incorrect after I `truncate` it. I can reproduce
this with the latest linux kernel
https://git.kernel.org/torvalds/t/linux-6.9-rc7.tar.gz
The following is the triggering script:
```
dd if=/dev/zero of=ext4-0.img bs=1M count=120
mkfs.ext4 ext4-0.img
g++ -static reproduce.c
losetup /dev/loop0 ext4-0.img
mkdir /root/mnt
./a.out
stat /root/mnt/a
```
After run the script, you will get the following outputs:
```
File: /root/mnt/a
Size: 0 Blocks: 82 IO Block: 1024 regular empty file
Device: 700h/1792d Inode: 12 Links: 1
Access: (0755/-rwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Context: system_u:object_r:unlabeled_t:s0
Access: 2024-05-08 11:47:48.000000000 +0000
Modify: 2024-05-08 11:47:48.000000000 +0000
Change: 2024-05-08 11:47:48.000000000 +0000
Birth: -
```
The size of file `a` is 0, yet it occupies 82 blocks. Normally, it should only
occupy 2 blocks.
The contents of `reproduce.c` :
```
#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <stddef.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
#include <dirent.h>
#include <string>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/wait.h>
#include <sys/xattr.h>
#include <sys/mount.h>
#include <sys/statfs.h>
#include <fcntl.h>
#define ALIGN 4096
void* align_alloc(size_t size) {
void *ptr = NULL;
int ret = posix_memalign(&ptr, ALIGN, size);
if (ret) {
printf("align error\n");
exit(1);
}
return ptr;
}
int main()
{
mount("/dev/loop0", "/root/mnt", "ext4", 0, "");
creat("/root/mnt/a", S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
int fd = open("/root/mnt/a", O_RDWR);
mount(NULL, "/root/mnt/", NULL, MS_REMOUNT, "nodelalloc");
sync();
char *buf = (char*)align_alloc(4096*20);
memset(buf, 'a' + 15, 4096*20);
write(fd, buf, 4096*10);
truncate("/root/mnt/a", 0);
close(fd);
return 0;
}
```
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next reply other threads:[~2024-05-08 13:33 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-08 13:33 bugzilla-daemon [this message]
2024-05-09 3:35 ` [Bug 218820] New: The empty file occupies incorrect blocks Theodore Ts'o
2024-05-09 3:35 ` [Bug 218820] " bugzilla-daemon
2024-05-09 6:35 ` bugzilla-daemon
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