Erofs as mount

[stepancheg]

Description

Containers need to work with some data mounted into /workdir.

This data can be downloaded on the server for example as targz and unpacked and bind-mounted. While downloading is often lightning fast, unpacking targz files is not so fast for example when filesystem is ext4, and targz contains a lot of small files.

It would be convenient if it would be possible to convert data to erofs and mount erofs blobs without unpacking.

This configuration

        {
            "destination": "/workdir",
            "type": "erofs",
            "source": "/downloads/files.erofs"
        },

results in warning

W1114 15:23:00.952578       1 vfs.go:992] ignoring unknown filesystem type "erofs"

Coming from there:

gvisor/runsc/boot/vfs.go

Line 979 in 56927bc

log.Warningf("ignoring unknown filesystem type %q", m.mount.Type)

This code looks like it is not too hard to allow erofs there?

Is this feature related to a specific bug?

No.

Do you have a specific solution in mind?

Allow "erofs" as mount type.

[ayushr2]

I agree that would be nice. PRs are appreciated.

As of now, EROFS can be used in the rootfs using dev.gvisor.spec.rootfs.* annotations:

gvisor/runsc/cmd/do.go

Lines 207 to 211 in 19abc45

	spec.Annotations = map[string]string{
	"dev.gvisor.spec.rootfs.source": c.erofs,
	"dev.gvisor.spec.rootfs.type": "erofs",
	"dev.gvisor.spec.rootfs.overlay": "memory",
	}

Or in bind mounts using runsc debug --mount flag:

gvisor/runsc/cmd/debug.go

Line 86 in 19abc45

f.StringVar(&d.mount, "mount", "", "Mount a filesystem (-mount fstype:source:destination).")

[mmishra100]

I created PR to address this issue, Please review if the approach is correct and need some refinement, or suggest if wrong approach