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 <tadeusz.struk@xxxxxxxxx> > --- > 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
