On 18/02/2025 11:40, Andreas Hindborg wrote:
"John Garry" <john.g.garry@xxxxxxxxxx> writes:
On 15/02/2025 10:58, Andreas Hindborg wrote:
When cloning a bio, the `bio.bi_vcnt` field is not cloned. This is a
problem if users want to perform bounds checks on the `bio.bi_io_vec`
field.
Is this fixing a potential problem? Or fixing a real issue?
It is fixing a problem I ran into in rnull, the rust null block
implementation. When running with debug assertions enabled, a bound
check on `bi_io_vec` fails for split bio, because `bio_vcnt` becomes
zero in the cloned bio.
I can work around this by not using a slice type to represent
`bi_io_vec` in rust, not a big deal.
But I am genuinely curious if there is a reason for not setting
`bi_vcnt` during a clone.
I think that it came from commit 59d276fe0 (with the addition of
bio_clone_fast()), where we assume that the cloned bio is not having the
bio_vec touched and so does not need to know bi_vcnt (or bi_max_vecs).
And it is inefficient to needlessly set bi_vcnt then.
As far as I can tell, it should be safe to
set. `bi_vcnt` being zero does not seem to have any effect other than to
puzzle developers debugging the code.
Maybe I missed something?
Thanks,
John
