On Fri, Apr 13, 2018 at 4:03 PM, cgxu519@xxxxxxx <cgxu519@xxxxxxx> wrote:
> 在 2018年4月13日，下午9:50，Miklos Szeredi <miklos@xxxxxxxxxx> 写道：
>>
>> On Fri, Apr 13, 2018 at 2:39 PM, Chengguang Xu <cgxu519@xxxxxxx> wrote:
>>> Check remount options and return error if there is any unchangeable
>>> option.
>>>
>>> Signed-off-by: Chengguang Xu <cgxu519@xxxxxxx>
>>> ---
>>> Changes since v3:
>>> - Fix error prone macro helper.
>>> - Make another new patch to only include code around.
>>>
>>> Changes since v2:
>>> - Introduce two macro helpers to simplify remount option validation.
>>>
>>> Changes since v1:
>>> - Refactor ovl_free_fs(), move config freeing operations to ovl_free_config().
>>>
>>> fs/overlayfs/super.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++---
>>> 1 file changed, 65 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
>>> index 0293635a..36587cbf 100644
>>> --- a/fs/overlayfs/super.c
>>> +++ b/fs/overlayfs/super.c
>>> @@ -230,6 +230,14 @@ static void ovl_destroy_inode(struct inode *inode)
>>> call_rcu(&inode->i_rcu, ovl_i_callback);
>>> }
>>>
>>> +static void ovl_free_config(struct ovl_config *config)
>>> +{
>>> + kfree(config->lowerdir);
>>> + kfree(config->upperdir);
>>> + kfree(config->workdir);
>>> + kfree(config->redirect_mode);
>>> +}
>>> +
>>> static void ovl_free_fs(struct ovl_fs *ofs)
>>> {
>>> unsigned i;
>>> @@ -249,10 +257,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
>>> kfree(ofs->lower_layers);
>>> kfree(ofs->lower_fs);
>>>
>>> - kfree(ofs->config.lowerdir);
>>> - kfree(ofs->config.upperdir);
>>> - kfree(ofs->config.workdir);
>>> - kfree(ofs->config.redirect_mode);
>>> + ovl_free_config(&ofs->config);
>>> if (ofs->creator_cred)
>>> put_cred(ofs->creator_cred);
>>> kfree(ofs);
>>> @@ -542,14 +547,70 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
>>> return ovl_parse_redirect_mode(config);
>>> }
>>>
>>> +static bool ovl_opt_bool_neq(bool new, bool old, const char *name)
>>> +{
>>> + if (new != old) {
>>> + pr_err("overlayfs: option \"%s\" cannot be %s on remount.\n",
>>> + name, new ? "enabled" : "disabled");
>>> + return true;
>>> + }
>>> + return false;
>>> +}
>>> +
>>> +static bool ovl_opt_string_neq(const char *new, const char *old,
>>> + const char *name)
>>> +{
>>> + if (new && (!old || strcmp(new, old))) {
>>> + pr_err("overlayfs: option \"%s\" cannot be changed on remount.\n",
>>> + name);
>>> + return true;
>>> + }
>>> + return false;
>>> +}
>>> +
>>> +#define ovl_config_opt_neq(old, new, name, type) \
>>> + ovl_opt_##type##_neq((old)->name, (new)->name, #name)
>>> +
>>> static int ovl_remount(struct super_block *sb, int *flags, char *data)
>>> {
>>> struct ovl_fs *ofs = sb->s_fs_info;
>>> + struct ovl_config *oc = &ofs->config;
>>> + struct ovl_config *nc;
>>> + int err;
>>>
>>> if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
>>> return -EROFS;
>>>
>>> + nc = kzalloc(sizeof(struct ovl_config), GFP_KERNEL);
>>> + if (!nc)
>>> + return -ENOMEM;
>>> +
>>> + nc->index = oc->index;
>>> + nc->nfs_export = oc->nfs_export;
>>
>> What about the other options?
>>
>> We should copy all of the old config to the new config here.
>>
>> If an option is not given, it should be assumed to stay the same as
>> the previous value (i.e. no need to supply options to remount that you
>> don't want to change).
>
> Yes, need to add ‘default_permissions’ later.
>
> For ‘redirect_dir’ and ‘redirect_follow’, the condition of changing is specifying
> new value to ‘redirect_mode’ and we have already checked it.
Ah, I missed the fact that ovl_opt_string_neq() takes care of the not
specified case.
Thanks,
Miklos
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