Re: [RFC PATCH v1 8/8] nfs: allow P2PDMA pages for O_DIRECT on RDMA mounts

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] nfs: build failure when CONFIG_NFS_V4 is disabled due to missing pnfs_enabled_sb() stub
--

commit e7be3531eda417e46246d357bf5c813741ed9450
Author: Pranjal Shrivastava <praan@google.com>

nfs: allow P2PDMA pages for O_DIRECT on RDMA mounts

This commit passes ITER_ALLOW_P2PDMA when extracting O_DIRECT pages on mounts
that use the RDMA transport and not pNFS. The RDMA transport moves such pages
only by DMA, and fails the RPC with -EREMOTEIO if the device cannot reach them.

> diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
> index a3c6e8f4ea06a..dbeb4f8274e3a 100644
> --- a/fs/nfs/direct.c
> +++ b/fs/nfs/direct.c
> @@ -157,14 +157,22 @@ static ssize_t nfs_direct_extract_pages(struct nfs_direct_req *dreq,
[ ... ]
>  	unsigned int npages, i;
>  	size_t pgbase;
>  
> -	result = iov_iter_extract_pages(iter, &pagevec, size, ~0U, 0, &pgbase);
> +	/* Allow P2PDMA pages only on RDMA mounts that do not use pNFS */
> +	if (server->nfs_client->cl_proto == XPRT_TRANSPORT_RDMA &&
> +	    !pnfs_enabled_sb(server))
> +		flags = ITER_ALLOW_P2PDMA;

[Severity: Low]
Will this cause a build failure when CONFIG_NFS_V4 is disabled?

The file fs/nfs/direct.c is compiled unconditionally for all NFS versions via
CONFIG_NFS_FS. However, pnfs_enabled_sb() is defined in fs/nfs/pnfs.h
exclusively inside an #if IS_ENABLED(CONFIG_NFS_V4) block:

fs/nfs/pnfs.h:pnfs_enabled_sb() {
	return nfss->pnfs_curr_ld != NULL;
}

Since there is no fallback provided in the #else block for configurations
without NFSv4, it seems any kernel configuration with CONFIG_NFS_FS=y
and CONFIG_NFS_V4=n might fail to build with an implicit function declaration.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261006233248.705086-1-praan@google.com?part=8