CAM(3) FreeBSD Library Functions Manual CAM(3)


cam_open_device, cam_open_spec_device, cam_open_btl, cam_open_pass, cam_close_device, cam_close_spec_device, cam_getccb, cam_send_ccb, cam_freeccb, cam_path_string, cam_device_dup, cam_device_copy, cam_get_deviceCAM user library


Common Access Method User Library (libcam, -lcam)


#include < stdio.h>
#include < camlib.h>

struct cam_device *
cam_open_device( const char *path, int flags);

struct cam_device *
cam_open_spec_device( const char *dev_name, int unit, int flags, struct cam_device *device);

struct cam_device *
cam_open_btl( path_id_t path_id, target_id_t target_id, lun_id_t target_lun, int flags, struct cam_device *device);

struct cam_device *
cam_open_pass( const char *path, int flags, struct cam_device *device);

cam_close_device( struct cam_device *dev);

cam_close_spec_device( struct cam_device *dev);

union ccb *
cam_getccb( struct cam_device *dev);

cam_send_ccb( struct cam_device *device, union ccb *ccb);

cam_freeccb( union ccb *ccb);

char *
cam_path_string( struct cam_device *dev, char *str, int len);

struct cam_device *
cam_device_dup( struct cam_device *device);

cam_device_copy( struct cam_device *src, struct cam_device *dst);

cam_get_device( const char *path, char *dev_name, int devnamelen, int *unit);


The CAM library consists of a number of functions designed to aid in programming with the CAM subsystem. This man page covers the basic set of library functions. More functions are documented in the man pages listed below.

Many of the CAM library functions use the cam_device structure:

struct cam_device { 
 char   device_path[MAXPATHLEN+1];/* 
         * Pathname of the 
         * device given by the 
         * user. This may be 
         * null if the user 
         * states the device 
         * name and unit number 
         * separately. 
 char  given_dev_name[DEV_IDLEN+1];/* 
           * Device name given by 
           * the user. 
 uint32_t given_unit_number;     /* 
           * Unit number given by 
           * the user. 
 char  device_name[DEV_IDLEN+1];/* 
        * Name of the device, 
        * e.g. 'pass' 
 uint32_t dev_unit_num; /* Unit number of the passthrough 
      * device associated with this 
      * particular device. 
 char  sim_name[SIM_IDLEN+1];/* 
            * Controller name, e.g.'ahc' 
 uint32_t sim_unit_number; /* Controller unit number */ 
 uint32_t bus_id;   /* Controller bus number */ 
 lun_id_t target_lun;  /* Logical Unit Number */ 
 target_id_t target_id;  /* Target ID */ 
 path_id_t path_id;  /* System SCSI bus number */ 
 uint16_t pd_type;  /* type of peripheral device */ 
 struct scsi_inquiry_data inq_data;  /* SCSI Inquiry data */ 
 uint8_t  serial_num[252]; /* device serial number */ 
 uint8_t  serial_num_len;  /* length of the serial number */ 
 uint8_t  sync_period;  /* Negotiated sync period */ 
 uint8_t  sync_offset;  /* Negotiated sync offset */ 
 uint8_t  bus_width;  /* Negotiated bus width */ 
 int  fd;   /* file descriptor for device */ 

cam_open_device() takes as arguments a string describing the device it is to open, and flags suitable for passing to open(2). The "path" passed in may actually be most any type of string that contains a device name and unit number to be opened. The string will be parsed by cam_get_device() into a device name and unit number. Once the device name and unit number are determined, a lookup is performed to determine the passthrough device that corresponds to the given device.

cam_open_spec_device() opens the pass(4) device that corresponds to the device name and unit number passed in. The flags should be flags suitable for passing to open(2). The device argument is optional. The user may supply pre-allocated space for the cam_device structure. If the device argument is NULL, cam_open_spec_device() will allocate space for the cam_device structure using malloc(3).

cam_open_btl() is similar to cam_open_spec_device(), except that it takes a SCSI bus, target and logical unit instead of a device name and unit number as arguments. The path_id argument is the CAM equivalent of a SCSI bus number. It represents the logical bus number in the system. The flags should be flags suitable for passing to open(2). As with cam_open_spec_device(), the device argument is optional.

cam_open_pass() takes as an argument the path of a pass(4) device to open. No translation or lookup is performed, so the path passed in must be that of a CAM pass(4) device. The flags should be flags suitable for passing to open(2). The device argument, as with cam_open_spec_device() and cam_open_btl(), should be NULL if the user wants the CAM library to allocate space for the cam_device structure. cam_close_device() frees the cam_device structure allocated by one of the above open() calls, and closes the file descriptor to the passthrough device. This routine should not be called if the user allocated space for the cam_device structure. Instead, the user should call cam_close_spec_device().

cam_close_spec_device() merely closes the file descriptor opened in one of the open() routines described above. This function should be called when the cam_device structure was allocated by the caller, rather than the CAM library.

cam_getccb() allocates a CCB using malloc(3) and sets fields in the CCB header using values from the cam_device structure.

cam_send_ccb() sends the given ccb to the device described in the cam_device structure.

cam_freeccb() frees CCBs allocated by cam_getccb().

cam_path_string() takes as arguments a cam_device structure, and a string with length len. It creates a colon-terminated printing prefix string similar to the ones used by the kernel. e.g.: "(cd0:ahc1:0:4:0): ". cam_path_string() will place at most len-1 characters into str. The len'th character will be the terminating ‘ \0’.

cam_device_dup() operates in a fashion similar to strdup(3). It allocates space for a cam_device structure and copies the contents of the passed-in device structure to the newly allocated structure.

cam_device_copy() copies the src structure to dst.

cam_get_device() takes a path argument containing a string with a device name followed by a unit number. It then breaks the string down into a device name and unit number, and passes them back in dev_name and unit, respectively. cam_get_device() can handle strings of the following forms, at least:


cam_get_device() is provided as a convenience function for applications that need to provide functionality similar to cam_open_device().


cam_open_device(), cam_open_spec_device(), cam_open_btl(), and cam_open_pass() return a pointer to a cam_device structure, or NULL if there was an error.

cam_getccb() returns an allocated and partially initialized CCB, or NULL if allocation of the CCB failed.

cam_send_ccb() returns a value of -1 if an error occurred, and errno is set to indicate the error.

cam_path_string() returns a filled printing prefix string as a convenience. This is the same str that is passed into cam_path_string().

cam_device_dup() returns a copy of the device passed in, or NULL if an error occurred.

cam_get_device() returns 0 for success, and -1 to indicate failure.

If an error is returned from one of the base CAM library functions described here, the reason for the error is generally printed in the global string cam_errbuf which is CAM_ERRBUF_SIZE characters long.


The CAM library first appeared in FreeBSD 3.0.


Kenneth Merry <ken@FreeBSD.org>


cam_open_device() does not check to see if the path passed in is a symlink to something. It also does not check to see if the path passed in is an actual pass(4) device. The former would be rather easy to implement, but the latter would require a definitive way to identify a device node as a pass(4) device.

Some of the functions are possibly mis-named or poorly named.

October 10, 1998 FreeBSD