Method push

virtio-devices/src/vsock/csm/txbuf.rs:50–82

Push a byte slice onto the ring-buffer. Either the entire source slice will be pushed to the ring-buffer, or none of it, if there isn't enough room, in which case `Err(Error::TxBufFull)` is returned.

(&mut self, src: &[u8])

    /// there isn't enough room, in which case `Err(Error::TxBufFull)` is returned.
    ///
    pub fn push(&mut self, src: &[u8]) -> Result<()> {
        // Error out if there's no room to push the entire slice.
        if self.len() + src.len() > Self::SIZE {
            return Err(Error::TxBufFull);
        }

        let data = self
            .data
            .get_or_insert_with(|| vec![0u8; Self::SIZE].into_boxed_slice());

        // Buffer head, as an offset into the data slice.
        let head_ofs = self.head.0 as usize % Self::SIZE;

        // Pushing a slice to this buffer can take either one or two slice copies: - one copy,
        // if the slice fits between `head_ofs` and `Self::SIZE`; or - two copies, if the
        // ring-buffer head wraps around.

        // First copy length: we can only go from the head offset up to the total buffer size.
        let len = std::cmp::min(Self::SIZE - head_ofs, src.len());
        data[head_ofs..(head_ofs + len)].copy_from_slice(&src[..len]);

        // If the slice didn't fit, the buffer head will wrap around, and pushing continues
        // from the start of the buffer (`&self.data[0]`).
        if len < src.len() {
            data[..(src.len() - len)].copy_from_slice(&src[len..]);
        }

        // Either way, we've just pushed exactly `src.len()` bytes, so that's the amount by
        // which the (wrapping) buffer head needs to move forward.
        self.head += Wrapping(src.len() as u32);

        Ok(())
    }

    /// Flush the contents of the ring-buffer to a writable stream.
    ///