Re: [PATCH 26/32] afs: Use fs_context to pass parameters over automount [ver #8]

[Goldwyn Rodrigues]

On 05/24/2018 07:08 PM, David Howells wrote:
> Alter the AFS automounting code to create and modify an fs_context struct
> when parameterising a new mount triggered by an AFS mountpoint rather than
> constructing device name and option strings.
> 
> Also remove the cell=, vol= and rwpath options as they are then redundant.
> The reason they existed is because the 'device name' may be derived
> literally from a mountpoint object in the filesystem, so default cell and
> parent-type information needed to be passed in by some other method from
> the automount routines.  The vol= option didn't end up being used.
> 
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Eric W. Biederman <ebiederm@xxxxxxxxxx>
> ---
> 
>  fs/afs/internal.h |    1 
>  fs/afs/mntpt.c    |  148 +++++++++++++++++++++++++++--------------------------
>  fs/afs/super.c    |   43 +--------------
>  3 files changed, 79 insertions(+), 113 deletions(-)
> 
> diff --git a/fs/afs/internal.h b/fs/afs/internal.h
> index eb6e75e00181..90af5001f8c8 100644
> --- a/fs/afs/internal.h
> +++ b/fs/afs/internal.h
> @@ -35,7 +35,6 @@ struct pagevec;
>  struct afs_call;
>  
>  struct afs_fs_context {
> -	bool			rwpath;		/* T if the parent should be considered R/W */
>  	bool			force;		/* T to force cell type */
>  	bool			autocell;	/* T if set auto mount operation */
>  	bool			dyn_root;	/* T if dynamic root */
> diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c
> index c45aa1776591..fc383d727552 100644
> --- a/fs/afs/mntpt.c
> +++ b/fs/afs/mntpt.c
> @@ -47,6 +47,8 @@ static DECLARE_DELAYED_WORK(afs_mntpt_expiry_timer, afs_mntpt_expiry_timed_out);
>  
>  static unsigned long afs_mntpt_expiry_timeout = 10 * 60;
>  
> +static const char afs_root_volume[] = "root.cell";
> +
>  /*
>   * no valid lookup procedure on this sort of dir
>   */
> @@ -68,107 +70,107 @@ static int afs_mntpt_open(struct inode *inode, struct file *file)
>  }
>  
>  /*
> - * create a vfsmount to be automounted
> + * Set the parameters for the proposed superblock.
>   */
> -static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
> +static int afs_mntpt_set_params(struct fs_context *fc, struct dentry *mntpt)
>  {
> -	struct afs_super_info *as;
> -	struct vfsmount *mnt;
> -	struct afs_vnode *vnode;
> -	struct page *page;
> -	char *devname, *options;
> -	bool rwpath = false;
> +	struct afs_fs_context *ctx = fc->fs_private;
> +	struct afs_vnode *vnode = AFS_FS_I(d_inode(mntpt));
> +	struct afs_cell *cell;
> +	const char *p;
>  	int ret;
>  
> -	_enter("{%pd}", mntpt);
> -
> -	BUG_ON(!d_inode(mntpt));
> -
> -	ret = -ENOMEM;
> -	devname = (char *) get_zeroed_page(GFP_KERNEL);
> -	if (!devname)
> -		goto error_no_devname;
> -
> -	options = (char *) get_zeroed_page(GFP_KERNEL);
> -	if (!options)
> -		goto error_no_options;
> -
> -	vnode = AFS_FS_I(d_inode(mntpt));
>  	if (test_bit(AFS_VNODE_PSEUDODIR, &vnode->flags)) {
>  		/* if the directory is a pseudo directory, use the d_name */
> -		static const char afs_root_cell[] = ":root.cell.";
>  		unsigned size = mntpt->d_name.len;
>  
> -		ret = -ENOENT;
> -		if (size < 2 || size > AFS_MAXCELLNAME)
> -			goto error_no_page;
> +		if (size < 2)
> +			return -ENOENT;
>  
> +		p = mntpt->d_name.name;
>  		if (mntpt->d_name.name[0] == '.') {
> -			devname[0] = '%';
> -			memcpy(devname + 1, mntpt->d_name.name + 1, size - 1);
> -			memcpy(devname + size, afs_root_cell,
> -			       sizeof(afs_root_cell));
> -			rwpath = true;
> -		} else {
> -			devname[0] = '#';
> -			memcpy(devname + 1, mntpt->d_name.name, size);
> -			memcpy(devname + size + 1, afs_root_cell,
> -			       sizeof(afs_root_cell));
> +			size--;
> +			p++;
> +			ctx->type = AFSVL_RWVOL;
> +			ctx->force = true;
> +		}
> +		if (size > AFS_MAXCELLNAME)
> +			return -ENAMETOOLONG;
> +
> +		cell = afs_lookup_cell(ctx->net, p, size, NULL, false);
> +		if (IS_ERR(cell)) {
> +			pr_err("kAFS: unable to lookup cell '%pd'\n", mntpt);
> +			return PTR_ERR(cell);
>  		}
> +		afs_put_cell(ctx->net, ctx->cell);
> +		ctx->cell = cell;
> +
> +		ctx->volname = afs_root_volume;
> +		ctx->volnamesz = sizeof(afs_root_volume) - 1;
>  	} else {
>  		/* read the contents of the AFS special symlink */
> +		struct page *page;
>  		loff_t size = i_size_read(d_inode(mntpt));
>  		char *buf;
>  
> -		ret = -EINVAL;
>  		if (size > PAGE_SIZE - 1)
> -			goto error_no_page;
> +			return -EINVAL;
>  
>  		page = read_mapping_page(d_inode(mntpt)->i_mapping, 0, NULL);
> -		if (IS_ERR(page)) {
> -			ret = PTR_ERR(page);
> -			goto error_no_page;
> -		}
> +		if (IS_ERR(page))
> +			return PTR_ERR(page);
>  
> -		ret = -EIO;
> -		if (PageError(page))
> -			goto error;
> +		if (PageError(page)) {
> +			put_page(page);
> +			return -EIO;
> +		}
>  
> -		buf = kmap_atomic(page);
> -		memcpy(devname, buf, size);
> -		kunmap_atomic(buf);
> +		buf = kmap(page);
> +		ret = vfs_set_fs_source(fc, buf, size);
> +		kunmap(page);
>  		put_page(page);
> -		page = NULL;
> +		if (ret < 0)
> +			return ret;
>  	}
>  
> -	/* work out what options we want */
> -	as = AFS_FS_S(mntpt->d_sb);
> -	if (as->cell) {
> -		memcpy(options, "cell=", 5);
> -		strcpy(options + 5, as->cell->name);
> -		if ((as->volume && as->volume->type == AFSVL_RWVOL) || rwpath)
> -			strcat(options, ",rwpath");
> -	}
> +	return 0;
> +}
>  
> -	/* try and do the mount */
> -	_debug("--- attempting mount %s -o %s ---", devname, options);
> -	mnt = vfs_submount(mntpt, &afs_fs_type, devname,
> -			   options, strlen(options) + 1);
> -	_debug("--- mount result %p ---", mnt);
> +/*
> + * create a vfsmount to be automounted
> + */
> +static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
> +{
> +	struct fs_context *fc;
> +	struct vfsmount *mnt;
> +	int ret;
> +
> +	BUG_ON(!d_inode(mntpt));
> +
> +	fc = vfs_new_fs_context(&afs_fs_type, mntpt, 0,
> +				FS_CONTEXT_FOR_SUBMOUNT);
> +	if (IS_ERR(fc))
> +		return ERR_CAST(fc);
> +
> +	ret = afs_mntpt_set_params(fc, mntpt);
> +	if (ret < 0)
> +		goto error_fc;
> +
> +	ret = vfs_get_tree(fc);
> +	if (ret < 0)
> +		goto error_fc;
> +
> +	mnt = vfs_create_mount(fc, 0);
> +	if (IS_ERR(mnt)) {
> +		ret = PTR_ERR(mnt);
> +		goto error_fc;
> +	}
>  
> -	free_page((unsigned long) devname);
> -	free_page((unsigned long) options);
> -	_leave(" = %p", mnt);
> +	put_fs_context(fc);
>  	return mnt;
>  

Why are you performing a put_fs_context(fc) in the success code path? Do
we not need a reference of fc anymore?


> -error:
> -	put_page(page);
> -error_no_page:
> -	free_page((unsigned long) options);
> -error_no_options:
> -	free_page((unsigned long) devname);
> -error_no_devname:
> -	_leave(" = %d", ret);
> +error_fc:
> +	put_fs_context(fc);
>  	return ERR_PTR(ret);
>  }
>  
-- 
Goldwyn