linux-kernel - Re: [PATCH] fs/exfat: add NFS export support

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Message-ID: <ZsNJNJE/bIWqsXl1@tissot.1015granger.net>
Date: Mon, 19 Aug 2024 09:31:32 -0400
From: Chuck Lever <chuck.lever@...cle.com>
To: andrii.polianytsia@...ballogic.com
Cc: linkinjeon@...nel.org, sj1557.seo@...sung.com, zach.malinowski@...min.com,
        artem.dombrovskyi@...ballogic.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, brauner@...nel.org,
        Sergii Boryshchenko <sergii.boryshchenko@...ballogic.com>,
        linux-nfs@...r.kernel.org
Subject: Re: [PATCH] fs/exfat: add NFS export support

[ ... adding linux-nfs@...r.kernel.org ]

On Mon, Aug 19, 2024 at 03:15:28PM +0300, andrii.polianytsia@...ballogic.com wrote:
> Add NFS export support to the exFAT filesystem by implementing
> the necessary export operations in fs/exfat/super.c. Enable
> exFAT filesystems to be exported and accessed over NFS, enhancing
> their utility in networked environments.
> 
> Introduce the exfat_export_ops structure, which includes
> functions to handle file handles and inode lookups necessary for NFS
> operations.

My memory is dim, but I think the reason that exporting exfat isn't
supported already is because it's file handles aren't persistent.

NFS requires that file handles remain the same across server
restarts or umount/mount cycles of the exported file system.


> Signed-off-by: Sergii Boryshchenko <sergii.boryshchenko@...ballogic.com>
> Signed-off-by: Andrii Polianytsia <andrii.polianytsia@...ballogic.com>
> ---
>  fs/exfat/super.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
> 
> diff --git a/fs/exfat/super.c b/fs/exfat/super.c
> index 323ecebe6f0e..cb6dcafc3007 100644
> --- a/fs/exfat/super.c
> +++ b/fs/exfat/super.c
> @@ -18,6 +18,7 @@
>  #include <linux/nls.h>
>  #include <linux/buffer_head.h>
>  #include <linux/magic.h>
> +#include <linux/exportfs.h>
>  
>  #include "exfat_raw.h"
>  #include "exfat_fs.h"
> @@ -195,6 +196,69 @@ static const struct super_operations exfat_sops = {
>  	.show_options	= exfat_show_options,
>  };
>  
> +/**
> + * exfat_export_get_inode - Get inode for export operations
> + * @sb: Superblock pointer
> + * @ino: Inode number
> + * @generation: Generation number
> + *
> + * Returns pointer to inode or error pointer in case of an error.
> + */
> +static struct inode *exfat_export_get_inode(struct super_block *sb, u64 ino,
> +	u32 generation)
> +{
> +	struct inode *inode = NULL;
> +
> +	if (ino == 0)
> +		return ERR_PTR(-ESTALE);
> +
> +	inode = ilookup(sb, ino);
> +	if (inode && generation && inode->i_generation != generation) {
> +		iput(inode);
> +		return ERR_PTR(-ESTALE);
> +	}
> +
> +	return inode;
> +}
> +
> +/**
> + * exfat_fh_to_dentry - Convert file handle to dentry
> + * @sb: Superblock pointer
> + * @fid: File identifier
> + * @fh_len: Length of the file handle
> + * @fh_type: Type of the file handle
> + *
> + * Returns dentry corresponding to the file handle.
> + */
> +static struct dentry *exfat_fh_to_dentry(struct super_block *sb,
> +	struct fid *fid, int fh_len, int fh_type)
> +{
> +	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
> +		exfat_export_get_inode);
> +}
> +
> +/**
> + * exfat_fh_to_parent - Convert file handle to parent dentry
> + * @sb: Superblock pointer
> + * @fid: File identifier
> + * @fh_len: Length of the file handle
> + * @fh_type: Type of the file handle
> + *
> + * Returns parent dentry corresponding to the file handle.
> + */
> +static struct dentry *exfat_fh_to_parent(struct super_block *sb,
> +	struct fid *fid, int fh_len, int fh_type)
> +{
> +	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
> +		exfat_export_get_inode);
> +}
> +
> +static const struct export_operations exfat_export_ops = {
> +	.encode_fh = generic_encode_ino32_fh,
> +	.fh_to_dentry = exfat_fh_to_dentry,
> +	.fh_to_parent = exfat_fh_to_parent,
> +};
> +
>  enum {
>  	Opt_uid,
>  	Opt_gid,
> @@ -633,6 +697,7 @@ static int exfat_fill_super(struct super_block *sb, struct fs_context *fc)
>  	sb->s_flags |= SB_NODIRATIME;
>  	sb->s_magic = EXFAT_SUPER_MAGIC;
>  	sb->s_op = &exfat_sops;
> +	sb->s_export_op = &exfat_export_ops;
>  
>  	sb->s_time_gran = 10 * NSEC_PER_MSEC;
>  	sb->s_time_min = EXFAT_MIN_TIMESTAMP_SECS;
> -- 
> 2.25.1
> 
> 

-- 
Chuck Lever