xrootd: extended attribute

[kiderrien]

It is possible to add extended attributes with xrootd and modify them.
Is it possible to do this with the go version of xrootd?

[sbinet]

hi there,

I am not well versed in this part of the code of go-hep (@EgorMatirov is the expert here).
but I believe this piece of code allows to get the xattrs:

package main

import (
	"context"
	"fmt"
	"log"

	"go-hep.org/x/hep/xrootd"
	"go-hep.org/x/hep/xrootd/xrdfs"
	"go-hep.org/x/hep/xrootd/xrdproto/query"
)

func main() {
	bkg := context.Background()

	cl, err := xrootd.NewClient(bkg, "ccxrootdgotest.in2p3.fr:9001", "gopher")
	if err != nil {
		log.Fatalf("could not create client: %v", err)
	}
	defer cl.Close()

	fs := cl.FS()
	f, err := fs.Open(bkg, "/tmp/dir1/file1.txt", xrdfs.OpenModeOwnerRead, xrdfs.OpenOptionsOpenRead)
	if err != nil {
		log.Fatalf("open error: %v", err)
	}
	defer f.Close(bkg)

	var (
		resp query.Response
		req  = query.Request{
			Query:  query.Space,
			Handle: f.Handle(),
			Args:   []byte("/tmp/dir1/file1.txt"),
		}
	)

	id, err := cl.Send(bkg, &resp, &req)
	if err != nil {
		log.Fatalf("space request error: %v", err)
	}
	fmt.Printf("sess: %s\n", id)
	// fmt.Printf("space: %q\n", resp.Data)

	req = query.Request{
		Query: query.XAttr,
		Args:  []byte("/tmp/dir1/file1.txt"),
	}

	id, err = cl.Send(bkg, &resp, &req)
	if err != nil {
		log.Fatalf("xattr request error: %v", err)
	}
	fmt.Printf("sess: %s\n", id)
	fmt.Printf("xattr: %v\n", string(resp.Data))

	// Output:
	// sess: ccxrootdgotest.in2p3.fr:9001
	// sess: ccxrootdgotest.in2p3.fr:9001
	// xattr: oss.cgroup=public&oss.type=f&oss.used=0&oss.mt=1530559859&oss.ct=1530603679&oss.at=1530559859&oss.u=*&oss.g=*&oss.fs=r&ofs.ap=a
}

as for modifying them, I don't think that's in. (yet?)

[sbinet]

so, the proposed plan of action would be to assess whether this (the above output) is what you're after for your rclone/xrootd integration.
then, assess what you need as modifications operations for that rclone/xrootd integration.

[beer4duke]

Thank you @sbinet for your quick feedback on this.
We need to find a way to implement various metadata information associated to the files.
Xrootd extended attributes seems the way to go for this:

• specific checksums
• timestamps modification after initial file creation as mtime cannot be set after the initial file creation
  -...

[beer4duke]

An update on this: we won't be able to use xrootd xattrs with the current eos 4.8.1 compiled against xrootd 4.x.

# xrdfs root://localhost query xattr /eos/instance/tmp/test_attr
[ERROR] Server responded with an error: [3005] Unable to fsctl /eos/instance/tmp/test_attr; Operation not supported

We need to wait for xrootd 5.x that has native support for extended attributes.

This means that we cannot use extended attributes for now, so no need to rush on this feature.
We'll find a workaround for the initial rclone xrootd implementation.

Thanks for your quick feedback @sbinet

Feel free to close this ticket as can hibernate for some time... for now