namazu has error when using O_DIRECT

[hxl1987]

Hello:
I wrote a program to verify the NAMAZU file system fault injection.
./nmz inspectors fs -mount-point /tmp/nmzfs-mnt -original-dir /tmp/nmzfs-orig -autopilot config.toml

The program are as follows:
test_fs.txt

I open a file that uses a direct IO option.
If the normal directory below /tmp/nmzfs-orig for write operation, you can write.But in the /tmp/nmzfs-mnt directory below operation, write will be wrong.
The error is:
write ./direct_io.data failed: Invalid argument
write ./direct_io.data failed: Invalid argument
write ./direct_io.data failed: Invalid argument

I checked the source code, found finally mounted by fusermount.So I added the direct_io option to fusermount in namazu/vendor/github.com/osrg/hookfs/hookfs/server.go.

pathFs := pathfs.NewPathNodeFs(hookfs, nil)
conn := nodefs.NewFileSystemConnector(pathFs.Root(), opts)
originalAbs, _ := filepath.Abs(hookfs.Original)
var the_opt = []string{"nonempty","direct_io"}
mOpts := &fuse.MountOptions{
AllowOther: true,
Name: hookfs.FsName,
FsName: originalAbs,
Options: the_opt,
}

But fusermount does not support the direct_io option.The error is:

[NMZ-INF] 16:34:40.02: fusermount the cmd is [/bin/fusermount /tmp/nmzfs-mnt -o nonempty,direct_io,allow_other,subtype=hookfs,fsname=/tmp/nmzfs-orig]
(at mount_linux.go:50)
[NMZ-WRN] 16:34:40.02: ignoring restPort: -1 (at endpoint.go:86)
[NMZ-WRN] 16:34:40.02: ignoring pbPort: -1 (at endpoint.go:97)
/bin/fusermount: mount failed: Invalid argument
[NMZ-CRT] 16:34:40.02: fusermount exited with code 256
(at fs.go:103)
[NMZ-CRT] 16:34:40.02: PANIC: fusermount exited with code 256
(at coreutil.go:49)
[NMZ-INF] 16:34:40.02: Hint: For debug info, please set "NMZ_DEBUG" to 1. (at coreutil.go:53)

Can you help me solve the problem? Looking forward to your early reply, thank you very much.

`

[AkihiroSuda]

Thank you a lot for reporting this issue.

AFAIK, FUSE does not support O_DIRECT.
https://sourceforge.net/p/fuse/mailman/message/27377600/
hanwen/go-fuse#146

So maybe we should support non-FUSE inspector as well (kprobes? NBD? iSCSI?)

PTAL @mitake

[AkihiroSuda]

If you are just interesting in injecting an error or non-interruptible sleeps (i.e. makes whole the system sleep, not single LWP), I suggest using "guru"-mode SystemTap

e245f5a

PTAL @mitake what do you suggest for injecting interruptible sleeps for filesystem operations, with support for O_DIRECT?

[mitake]

@AkihiroSuda I think the approach based on block device (nbd, iSCSI, qemu, etc) is too costly because correspondence between file accesses and block requests will be hard to be analyzed. kprobe based approach would be suitable for the case.