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@xxxxxxxxxxxxxxxxxxxx Reporter: zhangchi_seg@xxxxxxxxxxxxxxxx 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; } ``` -- You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.
