| Message ID | 20240605175953.2613260-8-joychakr@google.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | nvmem: Handle change of return type in reg_read/write() definition | expand |
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@google.com/ [2] https://lore.kernel.org/all/20240510082929.3792559-2-joychakr@google.com/ 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. 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. 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
On Thu, Jun 6, 2024 at 2:11 PM Dan Carpenter <dan.carpenter@linaro.org> 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@google.com/ > [2] https://lore.kernel.org/all/20240510082929.3792559-2-joychakr@google.com/ > > 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
On Thu, Jun 06, 2024 at 03:12:03PM +0530, Joy Chakraborty wrote: > > 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 . Returning non-zero is a bug. It won't break bin_attr_nvmem_read/write() but it will break other places like nvmem_access_with_keepouts(), __nvmem_cell_read() and nvmem_cell_prepare_write_buffer() where all non-zero returns from nvmem_reg_read() are treated as an error. > 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. If we're going to support partial writes, then it needs to be done all the way. We need to audit functions like at24_read() and remove the -EINVAL lines. 440 if (off + count > at24->byte_len) 441 return -EINVAL; It should be: if (off + count > at24->byte_len) count = at24->byte_len - off; Some drivers handle writing zero bytes as -EINVAL and some return 0. Those changes could be done before we change the API. You updated nvmem_access_with_keepouts() to handle negative returns but not zero returns so it could lead to a forever loop. regards, dan carpenter
On Thu, Jun 6, 2024 at 3:41 PM Dan Carpenter <dan.carpenter@linaro.org> wrote: > > On Thu, Jun 06, 2024 at 03:12:03PM +0530, Joy Chakraborty wrote: > > > 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 . > > Returning non-zero is a bug. It won't break bin_attr_nvmem_read/write() > but it will break other places like nvmem_access_with_keepouts(), > __nvmem_cell_read() and nvmem_cell_prepare_write_buffer() where all > non-zero returns from nvmem_reg_read() are treated as an error. > Yes, I will resend the patch to fix that. > > 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. > > If we're going to support partial writes, then it needs to be done all > the way. We need to audit functions like at24_read() and remove the > -EINVAL lines. > > 440 if (off + count > at24->byte_len) > 441 return -EINVAL; > > It should be: > > if (off + count > at24->byte_len) > count = at24->byte_len - off; > > Some drivers handle writing zero bytes as -EINVAL and some return 0. > Those changes could be done before we change the API. > Sure, we can do it in a phased manner like you suggested in another reply by creating new pointers and slowly moving each driver to the new pointer and then deprecating the old one. > You updated nvmem_access_with_keepouts() to handle negative returns but > not zero returns so it could lead to a forever loop. > Yes, that is a possible case. Will rework it. > regards, > dan carpenter > Thanks Joy
On 06/06/2024 09:41, Dan Carpenter wrote: > 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@google.com/ > [2]https://lore.kernel.org/all/20240510082929.3792559-2-joychakr@google.com/ > > 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. I agree with Dan, Lets fix the rmem_read and start working on the API rework in parallel. Am happy to pick the [1]. --srini
diff --git a/drivers/misc/eeprom/at25.c b/drivers/misc/eeprom/at25.c index 595ceb9a7126..73d60f80aea8 100644 --- a/drivers/misc/eeprom/at25.c +++ b/drivers/misc/eeprom/at25.c @@ -74,8 +74,8 @@ struct at25_data { #define io_limit PAGE_SIZE /* bytes */ -static int at25_ee_read(void *priv, unsigned int offset, - void *val, size_t count) +static ssize_t at25_ee_read(void *priv, unsigned int offset, + void *val, size_t count) { struct at25_data *at25 = priv; char *buf = val; @@ -147,7 +147,7 @@ static int at25_ee_read(void *priv, unsigned int offset, dev_dbg(&at25->spi->dev, "read %zu bytes at %d\n", count, offset); - return 0; + return count; } /* Read extra registers as ID or serial number */ @@ -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; } /*-------------------------------------------------------------------------*/
Change nvmem read/write function definition return type to ssize_t. Signed-off-by: Joy Chakraborty <joychakr@google.com> --- drivers/misc/eeprom/at25.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)