usb_get_configuration() uses a temporary buffer allocated on heap
to read USB configuration descriptor. The buffer is just nine
bytes an so it is a waste to allocate it on heap where it can be
allocated on stack with the rest of local variables. This
simplifies the code and minimises memory usage.
Signed-off-by: Michal Nazarewicz <[email protected]>
---
drivers/usb/core/config.c | 16 ++++------------
1 files changed, 4 insertions(+), 12 deletions(-)
diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 0d3af6a..78d3f87 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -722,13 +722,12 @@ int usb_get_configuration(struct usb_device *dev)
int ncfg = dev->descriptor.bNumConfigurations;
int result = 0;
unsigned int cfgno, length;
- unsigned char *buffer;
unsigned char *bigbuffer;
- struct usb_config_descriptor *desc;
+ struct usb_config_descriptor desc;
cfgno = 0;
if (dev->authorized == 0) /* Not really an error */
- goto out_not_authorized;
+ goto err;
result = -ENOMEM;
if (ncfg > USB_MAXCONFIG) {
dev_warn(ddev, "too many configurations: %d, "
@@ -751,17 +750,12 @@ int usb_get_configuration(struct usb_device *dev)
if (!dev->rawdescriptors)
goto err2;
- buffer = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL);
- if (!buffer)
- goto err2;
- desc = (struct usb_config_descriptor *)buffer;
-
result = 0;
for (; cfgno < ncfg; cfgno++) {
/* We grab just the first descriptor so we know how long
* the whole configuration is */
result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno,
- buffer, USB_DT_CONFIG_SIZE);
+ &desc, USB_DT_CONFIG_SIZE);
if (result < 0) {
dev_err(ddev, "unable to read config index %d "
"descriptor/%s: %d\n", cfgno, "start", result);
@@ -775,7 +769,7 @@ int usb_get_configuration(struct usb_device *dev)
result = -EINVAL;
goto err;
}
- length = max((int) le16_to_cpu(desc->wTotalLength),
+ length = max((int) le16_to_cpu(desc.wTotalLength),
USB_DT_CONFIG_SIZE);
/* Now that we know the length, get the whole thing */
@@ -810,8 +804,6 @@ int usb_get_configuration(struct usb_device *dev)
result = 0;
err:
- kfree(buffer);
-out_not_authorized:
dev->descriptor.bNumConfigurations = cfgno;
err2:
if (result == -ENOMEM)
--
Best regards, _ _
.o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michal "mina86" Nazarewicz (o o)
ooo +--<mina86-tlen.pl>--<jid:mina86-jabber.org>--ooO--(_)--Ooo--
On Sat, 17 Apr 2010, Michal Nazarewicz wrote:
> usb_get_configuration() uses a temporary buffer allocated on heap
> to read USB configuration descriptor. The buffer is just nine
> bytes an so it is a waste to allocate it on heap where it can be
> allocated on stack with the rest of local variables. This
> simplifies the code and minimises memory usage.
This is completely wrong. You are not allowed to do DMA to buffers on
the stack; some architectures are not capable of handling it.
Alan Stern
usb_gat_configuratio() used two pointers to point to the same
memory. Code simplified, by removing one of them.
Signed-off-by: Michal Nazarewicz <[email protected]>
---
drivers/usb/core/config.c | 10 ++++------
1 files changed, 4 insertions(+), 6 deletions(-)
> On Sat, 17 Apr 2010, Michal Nazarewicz wrote:
>> usb_get_configuration() uses a temporary buffer allocated on heap
>> to read USB configuration descriptor. The buffer is just nine
>> bytes an so it is a waste to allocate it on heap where it can be
>> allocated on stack with the rest of local variables. This
>> simplifies the code and minimises memory usage.
Alan Stern <[email protected]> writes:
> This is completely wrong. You are not allowed to do DMA to buffers on
> the stack; some architectures are not capable of handling it.
That makes sense; I haven't considered this thinking that copying nine
bytes by CPU, rather then using DMA, is not a big issue.
Still, the change proposed by attached commit does not suffer from DMA
issue and still simplify the code.
diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 0d3af6a..4b23e7f 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -722,7 +722,6 @@ int usb_get_configuration(struct usb_device *dev)
int ncfg = dev->descriptor.bNumConfigurations;
int result = 0;
unsigned int cfgno, length;
- unsigned char *buffer;
unsigned char *bigbuffer;
struct usb_config_descriptor *desc;
@@ -751,17 +750,16 @@ int usb_get_configuration(struct usb_device *dev)
if (!dev->rawdescriptors)
goto err2;
- buffer = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL);
- if (!buffer)
+ desc = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL);
+ if (!desc)
goto err2;
- desc = (struct usb_config_descriptor *)buffer;
result = 0;
for (; cfgno < ncfg; cfgno++) {
/* We grab just the first descriptor so we know how long
* the whole configuration is */
result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno,
- buffer, USB_DT_CONFIG_SIZE);
+ desc, USB_DT_CONFIG_SIZE);
if (result < 0) {
dev_err(ddev, "unable to read config index %d "
"descriptor/%s: %d\n", cfgno, "start", result);
@@ -810,7 +808,7 @@ int usb_get_configuration(struct usb_device *dev)
result = 0;
err:
- kfree(buffer);
+ kfree(desc);
out_not_authorized:
dev->descriptor.bNumConfigurations = cfgno;
err2:
--
Best regards, _ _
.o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michal "mina86" Nazarewicz (o o)
ooo +--<mina86-tlen.pl>--<jid:mina86-jabber.org>--ooO--(_)--Ooo--
On Sat, 17 Apr 2010, Michal Nazarewicz wrote:
> usb_gat_configuratio() used two pointers to point to the same
> memory. Code simplified, by removing one of them.
>
> Signed-off-by: Michal Nazarewicz <[email protected]>
> ---
> drivers/usb/core/config.c | 10 ++++------
> 1 files changed, 4 insertions(+), 6 deletions(-)
>
> > On Sat, 17 Apr 2010, Michal Nazarewicz wrote:
> >> usb_get_configuration() uses a temporary buffer allocated on heap
> >> to read USB configuration descriptor. The buffer is just nine
> >> bytes an so it is a waste to allocate it on heap where it can be
> >> allocated on stack with the rest of local variables. This
> >> simplifies the code and minimises memory usage.
>
> Alan Stern <[email protected]> writes:
> > This is completely wrong. You are not allowed to do DMA to buffers on
> > the stack; some architectures are not capable of handling it.
>
> That makes sense; I haven't considered this thinking that copying nine
> bytes by CPU, rather then using DMA, is not a big issue.
>
> Still, the change proposed by attached commit does not suffer from DMA
> issue and still simplify the code.
Yes, this is fine.
Alan Stern
This is a note to let you know that I've just added the patch titled
Subject: USB: core: config.c: usb_get_configuration() simplified
to my gregkh-2.6 tree. Its filename is
usb-core-config.c-usb_get_configuration-simplified.patch
This tree can be found at
http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/
>From [email protected] Thu Apr 29 16:05:40 2010
From: Michal Nazarewicz <[email protected]>
Date: Sat, 17 Apr 2010 17:12:58 +0200
Subject: USB: core: config.c: usb_get_configuration() simplified
To: Alan Stern <[email protected]>
Cc: [email protected], <[email protected]>, Greg Kroah-Hartman <[email protected]>
Message-ID: <[email protected]>
usb_gat_configuratio() used two pointers to point to the same
memory. Code simplified, by removing one of them.
Signed-off-by: Michal Nazarewicz <[email protected]>
Cc: Alan Stern <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/usb/core/config.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -735,7 +735,6 @@ int usb_get_configuration(struct usb_dev
int ncfg = dev->descriptor.bNumConfigurations;
int result = 0;
unsigned int cfgno, length;
- unsigned char *buffer;
unsigned char *bigbuffer;
struct usb_config_descriptor *desc;
@@ -764,17 +763,16 @@ int usb_get_configuration(struct usb_dev
if (!dev->rawdescriptors)
goto err2;
- buffer = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL);
- if (!buffer)
+ desc = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL);
+ if (!desc)
goto err2;
- desc = (struct usb_config_descriptor *)buffer;
result = 0;
for (; cfgno < ncfg; cfgno++) {
/* We grab just the first descriptor so we know how long
* the whole configuration is */
result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno,
- buffer, USB_DT_CONFIG_SIZE);
+ desc, USB_DT_CONFIG_SIZE);
if (result < 0) {
dev_err(ddev, "unable to read config index %d "
"descriptor/%s: %d\n", cfgno, "start", result);
@@ -823,7 +821,7 @@ int usb_get_configuration(struct usb_dev
result = 0;
err:
- kfree(buffer);
+ kfree(desc);
out_not_authorized:
dev->descriptor.bNumConfigurations = cfgno;
err2: