linux-kernel - Re: [PATCH v3 1/6] tpm: Move buffer handling from static inlines to real functions

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Date:   Sun, 05 Nov 2023 23:57:28 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Jerry Snitselaar <jsnitsel@...hat.com>
Cc:     linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        William Roberts <bill.c.roberts@...il.com>,
        Stefan Berger <stefanb@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Peter Huewe <peterhuewe@....de>,
        Mario Limonciello <mario.limonciello@....com>,
        Julien Gomes <julien@...sta.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/6] tpm: Move buffer handling from static inlines to
 real functions

On Thu, 2023-10-26 at 10:10 -0700, Jerry Snitselaar wrote:
> On Wed, Oct 25, 2023 at 08:35:55PM +0300, Jarkko Sakkinen wrote:
> > On Wed Oct 25, 2023 at 12:03 PM EEST, Jerry Snitselaar wrote:
> > > Reviewed-by: Jerry Snitselaar <jsnitsel@...hat.com>
> > 
> > On Wed, 2023-10-25 at 02:03 -0700, Jerry Snitselaar wrote:
> > > Reviewed-by: Jerry Snitselaar <jsnitsel@...hat.com>
> > > 
> > 
> > Thanks I'll add it to the next round.
> > 
> > For the tpm_buf_read(), I was thinking along the lines of:
> > 
> > /**
> >  * tpm_buf_read() - Read from a TPM buffer
> >  * @buf: &tpm_buf instance
> >  * @pos: position within the buffer
> >  * @count: the number of bytes to read
> >  * @output: the output buffer
> >  *
> >  * Read bytes from a TPM buffer, and update the position. Returns false when the
> >  * amount of bytes requested would overflow the buffer, which is expected to
> >  * only happen in the case of hardware failure.
> >  */
> > static bool tpm_buf_read(const struct tpm_buf *buf, off_t *pos, size_t count, void *output)
> > {
> >  off_t next = *pos + count;
> > 
> >  if (next >= buf->length) {
> >  pr_warn("%s: %lu >= %lu\n", __func__, next, *offset);
> >  return false;
> >  }
> > 
> >  memcpy(output, &buf->data[*pos], count);
> >  *offset = next;
> >  return true;
> > }
> > 
> > BR, Jarkko
> > 
> 
> Then the callers will check, and return -EIO?

Most likely. My thinking with boolean was that this way it
sort of documents that this function can have only single
possible error state.

If it was int there could be possibly some other error codes
to handle...

Just would prefer this based on my experience calling other
in-kernel functions. I often need to use lxr a lot just to
get full understanding of all possible POSIX codes...

BR, Jarkko