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cptofs: remount as read-only prior to exiting #534

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Nov 7, 2023
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cptofs: remount as read-only prior to exiting #534

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21 changes: 21 additions & 0 deletions tools/lkl/cptofs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -675,6 +675,27 @@ int main(int argc, char **argv)
break;
}

/* FIXME: Remouting as readonly seems to be required to make sure the filessytem is cleanly umounted. Otherwise the journal will be still dirty... */
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Looks good as a workaround, but I would like to investigate the root cause. Do you have a way to reproduce this?

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@Mic92 Mic92 Oct 11, 2023 •
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$ truncate -s 10G /tmp/foo.img
$ mkfs.ext4 /tmp/foo.img         
$ ./tools/lkl/cptofs -p -o 1000 -g 1000 -t ext4 -i /tmp/foo.img ./tools/lkl/tests  /

Now if you try to mount the image read-only, you can see hat it fails because of the unclean journal

$ mount -o ro /tmp/foo.img /mnt

The error will show up in dmesg.

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@tavip did you managed to reproduce the issue? This would block us updating lkl in NixOS, where we use it for building disk images without the need for KVM.

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I think I found the root cause but it is turning out more difficult to fix than I expected. Lets merge this for now. Thanks for the ping.

char dev_str[] = { "/dev/xxxxxxxx" };

snprintf(dev_str, sizeof(dev_str), "/dev/%08x", disk_id);
for (;;) {
ret = lkl_sys_mount(dev_str, mpoint, (char *)cla.fsimg_type, LKL_MS_RDONLY|LKL_MS_REMOUNT, NULL);
if (ret == 0)
break;
if (ret == -EBUSY) {
struct lkl_timespec ts = {
.tv_sec = 1,
.tv_nsec = 0,
};
lkl_sys_nanosleep((struct __lkl__kernel_timespec *)&ts, NULL);
continue;
} else if (ret < 0) {
fprintf(stderr, "cannot remount mount disk read-only: %s\n", lkl_strerror(ret));
break;
}
}

umount_ret = lkl_umount_dev(disk_id, cla.part, 0, 1000);
if (ret == 0)
ret = umount_ret;
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