[pbs-devel] [RFC pxar 4/20] fix #3174: metadata: impl fn to calc byte size

[Christian Ebner]

> On 27.09.2023 13:38 CEST Wolfgang Bumiller <w.bumiller at proxmox.com> wrote:
> 
>  
> On Fri, Sep 22, 2023 at 09:16:05AM +0200, Christian Ebner wrote:
> > Add a helper function to calculate the byte size of pxar Metadata
> > objects, needed to be able to recalculate offsets when creating archives
> > with appendix sections.
> > 
> > Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
> > ---
> >  src/lib.rs | 44 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> > 
> > diff --git a/src/lib.rs b/src/lib.rs
> > index 210c4b1..ed7ba40 100644
> > --- a/src/lib.rs
> > +++ b/src/lib.rs
> > @@ -144,6 +144,50 @@ impl Metadata {
> >      pub fn builder_from_stat(stat: &libc::stat) -> MetadataBuilder {
> >          MetadataBuilder::new(0).fill_from_stat(stat)
> >      }
> > +
> > +    /// Calculate the number of bytes when serialized in pxar archive
> > +    pub fn calculate_byte_len(&self) -> usize {
> 
> This looks like a maintenance nightmare with extra sprinkles.

;)

> 
> Can we instead create a specialized `SeqWrite` type that just counts
> bytes instead of actually writing anything and call the encoder's
> `encode_metadata()` with it?
> (Either by factorizing `encode_metadat()` out further or by creating an
> actual `EncoderImpl` instance with it...)

Yes, I will have a look on how to improve this and include this as well in the next version of the patch series, thx for the hints.

> 
> > +        let mut bytes = mem::size_of::<format::Header>();
> > +        bytes += mem::size_of_val(&self.stat);
> > +        for xattr in &self.xattrs {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(xattr);
> > +        }
> > +        for acl_user in &self.acl.users {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(acl_user);
> > +        }
> > +        for acl_group in &self.acl.groups {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(acl_group);
> > +        }
> > +        if let Some(group_obj) = &self.acl.group_obj {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(group_obj);
> > +        }
> > +        if let Some(default) = &self.acl.default {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(default);
> > +        }
> > +        for acl_default_user in &self.acl.default_users {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(acl_default_user);
> > +        }
> > +        for acl_default_group in &self.acl.default_groups {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(acl_default_group);
> > +        }
> > +        if let Some(fcaps) = &self.fcaps {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(fcaps);
> > +        }
> > +        if let Some(quota_project_id) = &self.quota_project_id {
> > +            bytes += mem::size_of::<format::Header>();
> > +            bytes += mem::size_of_val(quota_project_id);
> > +        }
> > +
> > +        bytes
> > +    }
> >  }
> >  
> >  impl From<MetadataBuilder> for Metadata {
> > -- 
> > 2.39.2