rt_device_write/read return data type as rt_ssize_t

rt_ssize_t can give negative error code, which follows the unix style correctly

libcpu/arm/AT91SAM7S/serial.c

@@ -215,7 +215,7 @@ static rt_err_t rt_serial_close(rt_device_t dev)
     return RT_EOK;
 }
 
-static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     struct rt_at91serial *serial = (struct rt_at91serial*)dev;
@@ -283,7 +283,7 @@ static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt
     return 0;
 }
 
-static rt_size_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     struct rt_at91serial *serial = (struct rt_at91serial*)dev;

libcpu/arm/s3c24x0/rtc.c

@@ -119,7 +119,7 @@ static rt_err_t rtc_close(rt_device_t dev)
     return RT_EOK;
 }
 
-static rt_size_t rtc_read(rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
+static rt_ssize_t rtc_read(rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
 {
     return RT_EOK;
 }

libcpu/arm/sep4020/serial.c

@@ -86,7 +86,7 @@ static rt_err_t rt_serial_close(rt_device_t dev)
     return RT_EOK;
 }
 
-static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     rt_err_t err_code;
@@ -144,7 +144,7 @@ static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt
     return (rt_uint32_t)ptr - (rt_uint32_t)buffer;
 }
 
-static rt_size_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     rt_err_t err_code;

libcpu/avr32/uc3/serial.c

@@ -59,7 +59,7 @@ static rt_err_t rt_serial_close(rt_device_t dev)
     return RT_EOK;
 }
 
-static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     rt_err_t err_code;
@@ -122,7 +122,7 @@ static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt
     return (rt_uint32_t)ptr - (rt_uint32_t)buffer;
 }
 
-static rt_size_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     rt_err_t err_code;

libcpu/blackfin/bf53x/serial.c

@@ -93,7 +93,7 @@ static rt_err_t rt_serial_close(rt_device_t dev)
     return RT_EOK;
 }
 
-static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     rt_err_t err_code;
@@ -151,7 +151,7 @@ static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt
     return (rt_uint32_t)ptr - (rt_uint32_t)buffer;
 }
 
-static rt_size_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     rt_err_t err_code;

libcpu/ppc/ppc405/serial.c

@@ -99,7 +99,7 @@ static rt_err_t rt_serial_control(rt_device_t dev, int cmd, void *args)
     return RT_EOK;
 }
 
-static rt_size_t rt_serial_read(rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_read(rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     struct rt_ppc405_serial* device;
@@ -156,7 +156,7 @@ static rt_size_t rt_serial_read(rt_device_t dev, rt_off_t pos, void* buffer, rt_
     return (rt_size_t)ptr - (rt_size_t)buffer;
 }
 
-static rt_size_t rt_serial_write(rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_write(rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
 {
     char *ptr;
     struct rt_ppc405_serial* device;

libcpu/unicore32/sep6200/serial.c

@@ -84,7 +84,7 @@ static rt_err_t rt_serial_close(rt_device_t dev)
     return RT_EOK;
 }
 
-static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     rt_err_t err_code;
@@ -142,7 +142,7 @@ static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt
     return (rt_uint32_t)ptr - (rt_uint32_t)buffer;
 }
 
-static rt_size_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     rt_err_t err_code;

libcpu/xilinx/microblaze/serial.c

@@ -144,7 +144,7 @@ static rt_err_t rt_serial_close(rt_device_t dev)
     return RT_EOK;
 }
 
-static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     struct rt_mb_uart_lite *serial = (struct rt_mb_uart_lite*)dev;
@@ -212,7 +212,7 @@ static rt_size_t rt_serial_read (rt_device_t dev, rt_off_t pos, void* buffer, rt
     return 0;
 }
 
-static rt_size_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
+static rt_ssize_t rt_serial_write (rt_device_t dev, rt_off_t pos, const void* buffer, rt_size_t size)
 {
     rt_uint8_t* ptr;
     struct rt_mb_uart_lite *serial = (struct rt_mb_uart_lite*)dev;