linux-ext4 - Re: [PATCH] create_inode: set xattrs to the root directory as well

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Date:   Fri, 17 Jul 2020 01:46:37 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Antoine Tenart <antoine.tenart@...tlin.com>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>, tytso@....edu,
        matthew.weber@...kwellcollins.com, thomas.petazzoni@...tlin.com
Subject: Re: [PATCH] create_inode: set xattrs to the root directory as well

On Jul 1, 2020, at 9:34 AM, Antoine Tenart <antoine.tenart@...tlin.com> wrote:
> 
> __populate_fs do copy the xattrs for all files and directories, but the
> root directory is skipped and as a result its extended attributes aren't
> set. This is an issue when using mkfs to build a full system image that
> can be used with SElinux in enforcing mode without making any runtime
> fix at first boot.
> 
> This patch adds logic to set the root directory's extended attributes.
> 
> Signed-off-by: Antoine Tenart <antoine.tenart@...tlin.com>
> ---
> misc/create_inode.c | 24 +++++++++++++++++++++++-
> 1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/misc/create_inode.c b/misc/create_inode.c
> index e8d1df6b55a5..0a6e4dc23d16 100644
> --- a/misc/create_inode.c
> +++ b/misc/create_inode.c
> @@ -820,7 +820,29 @@ static errcode_t __populate_fs(ext2_filsys fs, ext2_ino_t parent_ino,
> 
> 	for (i = 0; i < num_dents; free(dent[i]), i++) {
> 		name = dent[i]->d_name;
> -		if ((!strcmp(name, ".")) || (!strcmp(name, "..")))
> +		if (!strcmp(name, ".")) {

(style) despite what was previously in the code, I think it is clearer
to write "if (strcmp(name, ".") == 0)", because it doesn't read like
"if not string compare" since that incorrectly seems like the strings
are *not* matching.

> +			retval = ext2fs_namei(fs, root, parent_ino, ".", &ino);
> +			if (retval) {
> +				com_err(name, retval, 0);
> +					goto out;
> +			}
> +
> +			/*
> +			 * Take special care for the root directory, to copy its
> +			 * extended attributes.
> +			 */
> +			if (ino == root) {

Rather than checking this for every directory, it would be more efficient
to copy the root xattrs only at the start of the copy in populate_fs2(),
before the tree walk has started.  Something like:

	file_info.path_len = 0;
	file_info.path_max_len = 255;
	file_info.path = calloc(file_info.path_max_len, 1);

+	retval = set_inode_xattr(fs, parent_ino, source_dir);
+	if (retval) {
+		com_err(__func__, retval,
+			_("while copying xattrs on root directory"));
+		goto out;
+	}
+
	retval = __populate_fs(fs, parent_ino, source_dir, root, &hdlinks,
                               &file_info, fs_callbacks);

That is an even less code added, which is always good.

Cheers, Andreas






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