Re: [PATCH v2 1/2] fs: Improve and simplify copy_mount_options

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On Thu, Jun 16, 2016 at 1:38 AM, Willy Tarreau <w@xxxxxx> wrote:
> On Thu, Jun 16, 2016 at 10:20:38AM +0200, Willy Tarreau wrote:
>> However if the initial point was to avoid reading extra
>> pages most of the time, we could possibly consider that the string
>> copy is an optimization for the case where we have the information
>> available. Thus if !fstype || !(type->fs_flags & FS_BINARY_MOUNTDATA)
>> then we use copy_mount_options() otherwise we use copy_mount_string().
>> It will only leave the full page copy for mount --bind or -o remount
>> then.
>
> For example like this (not compile-tested either) :

I like this approach.  Al, is this okay with you?

--Andy

>
> diff --git a/fs/compat.c b/fs/compat.c
> index be6e48b..6407d40 100644
> --- a/fs/compat.c
> +++ b/fs/compat.c
> @@ -795,18 +795,26 @@ COMPAT_SYSCALL_DEFINE5(mount, const char __user *, dev_name,
>         void *options;
>         char *kernel_dev;
>         int retval;
> +       bool use_str = false;
> +       struct file_system_type *fstype;
>
>         kernel_type = copy_mount_string(type);
>         retval = PTR_ERR(kernel_type);
>         if (IS_ERR(kernel_type))
>                 goto out;
>
> +       if (kernel_type && (fstype = get_fs_type(kernel_type)) {
> +               if (!(fstype->fs_flags & FS_BINARY_MOUNTDATA))
> +                       use_str = true;
> +               put_filesystem(fstype);
> +       }
> +
>         kernel_dev = copy_mount_string(dev_name);
>         retval = PTR_ERR(kernel_dev);
>         if (IS_ERR(kernel_dev))
>                 goto out1;
>
> -       options = copy_mount_options(data);
> +       options = use_str ? copy_mount_string(data) : copy_mount_options(data);
>         retval = PTR_ERR(options);
>         if (IS_ERR(options))
>                 goto out2;
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 4fb1691..f14089d 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -2906,18 +2906,26 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
>         char *kernel_type;
>         char *kernel_dev;
>         void *options;
> +       bool use_str = false;
> +       struct file_system_type *fstype;
>
>         kernel_type = copy_mount_string(type);
>         ret = PTR_ERR(kernel_type);
>         if (IS_ERR(kernel_type))
>                 goto out_type;
>
> +       if (kernel_type && (fstype = get_fs_type(kernel_type)) {
> +               if (!(fstype->fs_flags & FS_BINARY_MOUNTDATA))
> +                       use_str = true;
> +               put_filesystem(fstype);
> +       }
> +
>         kernel_dev = copy_mount_string(dev_name);
>         ret = PTR_ERR(kernel_dev);
>         if (IS_ERR(kernel_dev))
>                 goto out_dev;
>
> -       options = copy_mount_options(data);
> +       options = use_str ? copy_mount_string(data) : copy_mount_options(data);
>         ret = PTR_ERR(options);
>         if (IS_ERR(options))
>                 goto out_data;



-- 
Andy Lutomirski
AMA Capital Management, LLC
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