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Subject: Re: Kernel OPS when using xattr
Date:   Thu, 3 Dec 2020 17:47:57 +0000
From:   Frank van der Linden <fllinden@amazon.com>
To:     Trond Myklebust <trondmy@hammerspace.com>
CC:     "tigran.mkrtchyan@desy.de" <tigran.mkrtchyan@desy.de>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
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On Thu, Dec 03, 2020 at 05:13:26PM +0000, Trond Myklebust wrote:
[...]
> You probably need this one in addition to the first patch.
> 8<----------------------------------------------------
> From fec77469f373fbccb292c2d522f2ebee3b9011a8 Mon Sep 17 00:00:00 2001
> From: Trond Myklebust <trond.myklebust@hammerspace.com>
> Date: Thu, 3 Dec 2020 12:04:51 -0500
> Subject: [PATCH] NFSv4.2: Fix up the get/listxattr calls to
>  rpc_prepare_reply_pages()
> 
> Ensure that both getxattr and listxattr page array are correctly
> aligned, and that getxattr correctly accounts for the page padding
> word.
> 
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  fs/nfs/nfs42xdr.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/nfs/nfs42xdr.c b/fs/nfs/nfs42xdr.c
> index 8432bd6b95f0..103978ff76c9 100644
> --- a/fs/nfs/nfs42xdr.c
> +++ b/fs/nfs/nfs42xdr.c
> @@ -191,7 +191,7 @@
> 
>  #define encode_getxattr_maxsz   (op_encode_hdr_maxsz + 1 + \
>                                  nfs4_xattr_name_maxsz)
> -#define decode_getxattr_maxsz   (op_decode_hdr_maxsz + 1 + 1)
> +#define decode_getxattr_maxsz   (op_decode_hdr_maxsz + 1 +
> pagepad_maxsz)
>  #define encode_setxattr_maxsz   (op_encode_hdr_maxsz + \
>                                  1 + nfs4_xattr_name_maxsz + 1)
>  #define decode_setxattr_maxsz   (op_decode_hdr_maxsz +
> decode_change_info_maxsz)
> @@ -1476,17 +1476,18 @@ static void nfs4_xdr_enc_getxattr(struct
> rpc_rqst *req, struct xdr_stream *xdr,
>         struct compound_hdr hdr = {
>                 .minorversion = nfs4_xdr_minorversion(&args-
> >seq_args),
>         };
> +       uint32_t replen;
>         size_t plen;
> 
>         encode_compound_hdr(xdr, req, &hdr);
>         encode_sequence(xdr, &args->seq_args, &hdr);
>         encode_putfh(xdr, args->fh, &hdr);
> +       replen = hdr.replen + op_decode_hdr_maxsz + 1;
>         encode_getxattr(xdr, args->xattr_name, &hdr);
> 
>         plen = args->xattr_len ? args->xattr_len : XATTR_SIZE_MAX;
> 
> -       rpc_prepare_reply_pages(req, args->xattr_pages, 0, plen,
> -           hdr.replen);
> +       rpc_prepare_reply_pages(req, args->xattr_pages, 0, plen,
> replen);
>         req->rq_rcv_buf.flags |= XDRBUF_SPARSE_PAGES;
> 
>         encode_nops(&hdr);
> @@ -1520,14 +1521,15 @@ static void nfs4_xdr_enc_listxattrs(struct
> rpc_rqst *req,
>         struct compound_hdr hdr = {
>                 .minorversion = nfs4_xdr_minorversion(&args-
> >seq_args),
>         };
> +       uint32_t replen;
> 
>         encode_compound_hdr(xdr, req, &hdr);
>         encode_sequence(xdr, &args->seq_args, &hdr);
>         encode_putfh(xdr, args->fh, &hdr);
> +       replen = hdr.replen + op_decode_hdr_maxsz + 2 + 1;
>         encode_listxattrs(xdr, args, &hdr);
> 
> -       rpc_prepare_reply_pages(req, args->xattr_pages, 0, args-
> >count,
> -           hdr.replen);
> +       rpc_prepare_reply_pages(req, args->xattr_pages, 0, args-
> >count, replen);
> 
>         encode_nops(&hdr);
>  }
> --
> 2.28.0

Hm.. that doesn't seem to match other, similar functionality.
Why is the additional padding and op_decode_hdr_maxsz needed?

- Frank