On Thu, Nov 15, 2018 at 12:42:22PM -0800, Tadeusz Struk wrote:
> Currently to read a response from the TPM device an application needs
> provide big enough buffer for the whole response and read it in one go.
> The application doesn't know how big the response it beforehand so it
> always needs to maintain a 4K buffer and read the max (4K).
> In case if the user of the TSS library doesn't provide big enough
> buffer the TCTI spec says that the library should set the required
> size and return TSS2_TCTI_RC_INSUFFICIENT_BUFFER error code so that the
> application could allocate a bigger buffer and call receive again.
> To make it possible in the TSS library, this requires being able to do
> partial reads from the driver.
> The library would read the 10 bytes header first to get the actual size
> of the response from the header, and then read the rest of the response.
>
> This patch adds support for partial reads, i.e. the user can read the
> response in one or multiple reads, until the whole response is consumed.
> The user can also read only part of the response and ignore
> the rest by issuing a new write to send a new command.
>
> Signed-off-by: Tadeusz Struk <[email protected]>
> ---
> The usecase is implemented in this TSS commit:
> https://github.com/tpm2-software/tpm2-tss/commit/ce982f67a67dc08e24683d30b05800648d8a264c
>
> Changes in v3:
> - Remove link to usecase implemented in TSS out of the commit message.
> - Update the conddition in tpm_common_poll() to take into account
> the partial_data also.
>
> Changes in v2:
> - Allow writes after only partial response is consumed to maintain
> backwords compatibility.
> ---
> drivers/char/tpm/tpm-dev-common.c | 41
> ++++++++++++++++++++++++++++---------
> drivers/char/tpm/tpm-dev.h | 2 ++
> 2 files changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm-dev-common.c
> b/drivers/char/tpm/tpm-dev-common.c
> index 99b5133a9d05..5d43b0c28565 100644
> --- a/drivers/char/tpm/tpm-dev-common.c
> +++ b/drivers/char/tpm/tpm-dev-common.c
> @@ -64,6 +64,7 @@ static void tpm_timeout_work(struct work_struct *work)
>
> mutex_lock(&priv->buffer_mutex);
> priv->data_pending = 0;
> + priv->partial_data = 0;
> memset(priv->data_buffer, 0, sizeof(priv->data_buffer));
> mutex_unlock(&priv->buffer_mutex);
> wake_up_interruptible(&priv->async_wait);
> @@ -90,22 +91,39 @@ ssize_t tpm_common_read(struct file *file, char __user
> *buf,
> ssize_t ret_size = 0;
> int rc;
>
> - del_singleshot_timer_sync(&priv->user_read_timer);
> - flush_work(&priv->timeout_work);
> mutex_lock(&priv->buffer_mutex);
> + if (priv->data_pending || priv->partial_data) {
> + if (*off == 0)
> + priv->partial_data = priv->data_pending;
> +
> + ret_size = min_t(ssize_t, size, priv->partial_data);
> + if (ret_size <= 0) {
> + ret_size = 0;
> + priv->data_pending = 0;
> + priv->partial_data = 0;
> + goto out;
> + }
>
> - if (priv->data_pending) {
> - ret_size = min_t(ssize_t, size, priv->data_pending);
> - if (ret_size > 0) {
> - rc = copy_to_user(buf, priv->data_buffer, ret_size);
> - memset(priv->data_buffer, 0, priv->data_pending);
> - if (rc)
> - ret_size = -EFAULT;
> + rc = copy_to_user(buf, priv->data_buffer + *off, ret_size);
> + if (rc) {
> + memset(priv->data_buffer, 0, TPM_BUFSIZE);
> + priv->partial_data = 0;
> + ret_size = -EFAULT;
> + } else {
> + memset(priv->data_buffer + *off, 0, ret_size);
> + priv->partial_data -= ret_size;
> + *off += ret_size;
You could drop these memset() calls and also one from
tpm_timeout_work(). The call could be done once in the beginning of
tpm_common_write() instead of having three different call sites.
Replacing two memsets with one could be a prepending commit.
> }
>
> priv->data_pending = 0;
> }
>
> +out:
> + if (!priv->partial_data) {
> + *off = 0;
> + del_singleshot_timer_sync(&priv->user_read_timer);
> + flush_work(&priv->timeout_work);
> + }
> mutex_unlock(&priv->buffer_mutex);
> return ret_size;
> }
> @@ -150,6 +168,9 @@ ssize_t tpm_common_write(struct file *file, const char
> __user *buf,
> goto out;
> }
>
> + priv->partial_data = 0;
> + *off = 0;
> +
> /*
> * If in nonblocking mode schedule an async job to send
> * the command return the size.
> @@ -184,7 +205,7 @@ __poll_t tpm_common_poll(struct file *file, poll_table
> *wait)
>
> poll_wait(file, &priv->async_wait, wait);
>
> - if (priv->data_pending)
> + if (priv->data_pending || priv->partial_data)
> mask = EPOLLIN | EPOLLRDNORM;
> else
> mask = EPOLLOUT | EPOLLWRNORM;
> diff --git a/drivers/char/tpm/tpm-dev.h b/drivers/char/tpm/tpm-dev.h
> index a126b575cb8c..a2ca6a7a06f1 100644
> --- a/drivers/char/tpm/tpm-dev.h
> +++ b/drivers/char/tpm/tpm-dev.h
> @@ -11,6 +11,8 @@ struct file_priv {
>
> /* Holds the amount of data passed or an error code from async op */
> ssize_t data_pending;
> + /* For partial reads, holds the reminder of a response */
> + ssize_t partial_data;
Naming becomes a mess and the comment for data_pending variable is
incorrect as it is also used for synchronous operation.
Maybe add a prepending commit to rename it as
/* Holds the resul of the tpm_transmit() last call. */
ssize_t transmit_result;
That is at least clear and obvious on what it contains.
The comment for partial_data is incorrect as the variable does not
contain any data.
We could use declare:
/* Holds the count how much of the response is still unread. */
size_t response_pending;
Observe another remark from your commit: there is no reaso to ssize_t as
the type as the value should never be a negative number.
/Jarkko
