Re: [PATCH v2 2/9] mm/mshare: pre-populate msharefs with information file

Darrick J. Wong
2022-06-30T21:37:58Z

On Wed, Jun 29, 2022 at 04:53:53PM -0600, Khalid Aziz wrote:
> Users of mshare feature to share page tables need to know the size
> and alignment requirement for shared regions. Pre-populate msharefs
> with a file, mshare_info, that provides this information.
>
> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
> ---
> mm/mshare.c | 62 +++++++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 48 insertions(+), 14 deletions(-)
>
> diff --git a/mm/mshare.c b/mm/mshare.c
> index c8fab3869bab..3e448e11c742 100644
> --- a/mm/mshare.c
> +++ b/mm/mshare.c
> @@ -25,8 +25,8 @@
> static struct super_block *msharefs_sb;
>
> static const struct file_operations msharefs_file_operations = {
> - .open = simple_open,
> - .llseek = no_llseek,
> + .open = simple_open,
> + .llseek = no_llseek,

I feel like there's a lot of churn between the previous patch and this
one that could have been in the previous patch.

> };
>
> static int
> @@ -42,23 +42,52 @@ msharefs_d_hash(const struct dentry *dentry, struct qstr *qstr)
> return 0;
> }
>
> +static void
> +mshare_evict_inode(struct inode *inode)
> +{
> + clear_inode(inode);
> +}
> +
> static const struct dentry_operations msharefs_d_ops = {
> .d_hash = msharefs_d_hash,
> };
>
> +static ssize_t
> +mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
> + loff_t *ppos)
> +{
> + char s[80];
> +
> + sprintf(s, "%ld", PGDIR_SIZE);

SO what is this "mshare_info" file supposed to reveal? Hugepage size?
I wonder why this isn't exported in struct mshare_info?

> + return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
> +}
> +
> +static const struct file_operations mshare_info_ops = {
> + .read = mshare_info_read,
> + .llseek = noop_llseek,
> +};
> +
> +static const struct super_operations mshare_s_ops = {
> + .statfs = simple_statfs,
> + .evict_inode = mshare_evict_inode,
> +};
> +
> static int
> msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
> {
> - static const struct tree_descr empty_descr = {""};
> + static const struct tree_descr mshare_files[] = {
> + [2] = { "mshare_info", &mshare_info_ops, 0444},
> + {""},
> + };
> int err;
>
> - sb->s_d_op = &msharefs_d_ops;
> - err = simple_fill_super(sb, MSHARE_MAGIC, &empty_descr);
> - if (err)
> - return err;
> -
> - msharefs_sb = sb;
> - return 0;
> + err = simple_fill_super(sb, MSHARE_MAGIC, mshare_files);
> + if (!err) {
> + msharefs_sb = sb;
> + sb->s_d_op = &msharefs_d_ops;
> + sb->s_op = &mshare_s_ops;
> + }
> + return err;
> }
>
> static int
> @@ -84,20 +113,25 @@ static struct file_system_type mshare_fs = {
> .kill_sb = kill_litter_super,
> };
>
> -static int
> +static int __init
> mshare_init(void)
> {
> int ret = 0;
>
> ret = sysfs_create_mount_point(fs_kobj, "mshare");
> if (ret)
> - return ret;
> + goto out;
>
> ret = register_filesystem(&mshare_fs);
> - if (ret)
> + if (ret) {
> sysfs_remove_mount_point(fs_kobj, "mshare");
> + goto out;
> + }
> +
> + return 0;
>
> +out:
> return ret;
> }
>
> -fs_initcall(mshare_init);
> +core_initcall(mshare_init);
> --
> 2.32.0
>