bufinfo_t structure (Solaris Dynamic Tracing Guide)

Solaris Dynamic Tracing Guide

`bufinfo_t` structure

The bufinfo_t structure is the abstraction that describes an I/O request. The buffer corresponding to an I/O request is pointed to by args[0] in the start, done, wait-start, and wait-done probes. The bufinfo_t structure definition is as follows:

typedef struct bufinfo {
	int b_flags;                    /* flags */
	size_t b_bcount;                /* number of bytes */
	caddr_t b_addr;                 /* buffer address */
	uint64_t b_blkno;               /* expanded block # on device */
	uint64_t b_lblkno;              /* block # on device */
	size_t b_resid;                 /* # of bytes not transferred */
	size_t b_bufsize;               /* size of allocated buffer */ 
	caddr_t b_iodone;               /* I/O completion routine */
	dev_t b_edev;                   /* extended device */
 } bufinfo_t;

The b_flags member indicates the state of the I/O buffer, and consists of a bitwise-or of different state values. The valid state values are in Table 27–3.

Table 27–3 b_flags Values


`B_DONE`	Indicates that the data transfer has completed.
`B_ERROR`	Indicates an I/O transfer error. It is set in conjunction with the `b_error` field.
`B_PAGEIO`	Indicates that the buffer is being used in a paged I/O request. See the description of the `b_addr` field for more information.
`B_PHYS`	Indicates that the buffer is being used for physical (direct) I/O to a user data area.
`B_READ`	Indicates that data is to be read from the peripheral device into main memory.
`B_WRITE`	Indicates that the data is to be transferred from main memory to the peripheral device.
`B_ASYNC`	The I/O request is asynchronous, and will not be waited upon. The `wait-start` and `wait-done` probes don't fire for asynchronous I/O requests. Note that some I/Os directed to be asynchronous might not have `B_ASYNC` set: the asynchronous I/O subsystem might implement the asynchronous request by having a separate worker thread perform a synchronous I/O operation.

The b_bcount field is the number of bytes to be transferred as part of the I/O request.

The b_addr field is the virtual address of the I/O request, unless B_PAGEIO is set. The address is a kernel virtual address unless B_PHYS is set, in which case it is a user virtual address. If B_PAGEIO is set, the b_addr field contains kernel private data. Exactly one of B_PHYS and B_PAGEIO can be set, or neither flag will be set.

The b_lblkno field identifies which logical block on the device is to be accessed. The mapping from a logical block to a physical block (such as the cylinder, track, and so on) is defined by the device.

The b_resid field is set to the number of bytes not transferred because of an error.

The b_bufsize field contains the size of the allocated buffer.

The b_iodone field identifies a specific routine in the kernel that is called when the I/O is complete.

The b_error field may hold an error code returned from the driver in the event of an I/O error. b_error is set in conjunction with the B_ERROR bit set in the b_flags member.

The b_edev field contains the major and minor device numbers of the device accessed. Consumers may use the D subroutines getmajor() and getminor() to extract the major and minor device numbers from the b_edev field.