On Thu, Jun 6, 2024 at 2:11 PM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
>
> On Wed, Jun 05, 2024 at 05:59:51PM +0000, Joy Chakraborty wrote:
> > @@ -195,10 +195,11 @@ static struct attribute *sernum_attrs[] = {
> > };
> > ATTRIBUTE_GROUPS(sernum);
> >
> > -static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
> > +static ssize_t at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
> > {
> > struct at25_data *at25 = priv;
> > size_t maxsz = spi_max_transfer_size(at25->spi);
> > + size_t bytes_written = count;
> > const char *buf = val;
> > int status = 0;
> > unsigned buf_size;
> > @@ -313,7 +314,7 @@ static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
> > mutex_unlock(&at25->lock);
> >
> > kfree(bounce);
> > - return status;
> > + return status < 0 ? status : bytes_written;
> > }
>
> So the original bug was that rmem_read() is returning positive values
> on success instead of zero[1]. That started a discussion about partial
> reads which resulted in changing the API to support partial reads[2].
> That patchset broke the build. This patchset is trying to fix the
> build breakage.
>
> [1] https://lore.kernel.org/all/20240206042408.224138-1-joychakr@xxxxxxxxxx/
> [2] https://lore.kernel.org/all/20240510082929.3792559-2-joychakr@xxxxxxxxxx/
>
> The bug in rmem_read() is still not fixed. That needs to be fixed as
> a stand alone patch. We can discuss re-writing the API separately.
>
True, fixing the return type would fix that as well is what I thought
but maybe yes we need to fix that separately as well.
> These functions are used internally and exported to the user through
> sysfs via bin_attr_nvmem_read/write(). For internal users partial reads
> should be treated as failure. What are we supposed to do with a partial
> read? I don't think anyone has asked for partial reads to be supported
> from sysfs either except Greg was wondering about it while reading the
> code.
>
> Currently, a lot of drivers return -EINVAL for partial read/writes but
> some return success. It is a bit messy. But this patchset doesn't
> really improve anything. In at24_read() we check if it's going to be a
> partial read and return -EINVAL. Below we report a partial read as a
> full read. It's just a more complicated way of doing exactly what we
> were doing before.
Currently what drivers return is up to their interpretation of int
return type, there are a few drivers which also return the number of
bytes written/read already like
drivers/misc/mchp_pci1xxxx/mchp_pci1xxxx_otpe2p.c .
The objective of the patch was to handle partial reads and errors at
the nvmem core and instead of leaving it up to each nvmem provider by
providing a better return value to nvmem providers.
Regarding drivers/misc/eeprom/at25.c which you pointed below, that is
a problem in my code change. I missed that count was modified later on
and should initialize bytes_written to the new value of count, will
fix that when I come up with the new patch.
I agree that it does not improve anything for a lot of nvmem providers
for example the ones which call into other reg_map_read/write apis
which do not return the number of bytes read/written but it does help
us do better error handling at the nvmem core layer for nvmem
providers who can return the valid number of bytes read/written.
Please let me know if you have any other suggestions on how to handle
this better.
Thanks
Joy
>
> drivers/misc/eeprom/at25.c
> 198 static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
> 199 {
> 200 struct at25_data *at25 = priv;
> 201 size_t maxsz = spi_max_transfer_size(at25->spi);
> New: size_t bytes_written = count;
> ^^^^^^^^^^^^^^^^^^^^^
> This is not the number of bytes written.
>
> 202 const char *buf = val;
> 203 int status = 0;
> 204 unsigned buf_size;
> 205 u8 *bounce;
> 206
> 207 if (unlikely(off >= at25->chip.byte_len))
> 208 return -EFBIG;
> 209 if ((off + count) > at25->chip.byte_len)
> 210 count = at25->chip.byte_len - off;
> ^^^^^
> This is.
>
> 211 if (unlikely(!count))
> 212 return -EINVAL;
> 213
> 214 /* Temp buffer starts with command and address */
> 215 buf_size = at25->chip.page_size;
> 216 if (buf_size > io_limit)
> 217 buf_size = io_limit;
> 218 bounce = kmalloc(buf_size + at25->addrlen + 1, GFP_KERNEL);
> 219 if (!bounce)
> 220 return -ENOMEM;
> 221
>
> regards,
> dan carpenter
