The I/O kernel services fall into the following categories: Block I/O services, Buffer Cache services, Character I/O services, Interrupt Management services, Memory Buffer (mbuf) services, DMA Management services.
The Block I/O kernel services are:
| iodone | Performs block I/O completion processing. |
| iowait | Waits for block I/O completion. |
| uphysio | Performs character I/O for a block device using a uio structure. |
The Block I/O Buffer Cache Kernel Services: Overview describes how to manage the buffer cache with the Buffer Cache kernel services. The Buffer Cache kernel services are:
| bawrite | Writes the specified buffer's data without waiting for I/O to complete. |
| bdwrite | Releases the specified buffer after marking it for delayed write. |
| bflush | Flushes all write-behind blocks on the specified device from the buffer cache. |
| binval | Invalidates all of the specified device's blocks in the buffer cache. |
| blkflush | Flushes the specified block if it is in the buffer cache. |
| bread | Reads the specified block's data into a buffer. |
| breada | Reads in the specified block and then starts I/O on the read-ahead block. |
| brelse | Frees the specified buffer. |
| bwrite | Writes the specified buffer's data. |
| clrbuf | Sets the memory for the specified buffer structure's buffer to all zeros. |
| getblk | Assigns a buffer to the specified block. |
| geteblk | Allocates a free buffer. |
| geterror | Determines the completion status of the buffer. |
| purblk | Purges the specified block from the buffer cache. |
The Character I/O kernel services are:
| getc | Retrieves a character from a character list. |
| getcb | Removes the first buffer from a character list and returns the address of the removed buffer. |
| getcbp | Retrieves multiple characters from a character buffer and places them at a designated address. |
| getcf | Retrieves a free character buffer. |
| getcx | Returns the character at the end of a designated list. |
| pincf | Manages the list of free character buffers. |
| putc | Places a character at the end of a character list. |
| putcb | Places a character buffer at the end of a character list. |
| putcbp | Places several characters at the end of a character list. |
| putcf | Frees a specified buffer. |
| putcfl | Frees the specified list of buffers. |
| putcx | Places a character on a character list. |
| waitcfree | Checks the availability of a free character buffer. |
The operating system provides the following set of kernel services for managing interrupts. See Understanding Interrupts for a description of these services:
| i_clear | Removes an interrupt handler from the system. |
| i_reset | Resets the system's hardware interrupt latches. |
| i_sched | Schedules off-level processing. |
| i_mask | Disables an interrupt level. |
| i_unmask | Enables an interrupt level. |
| i_disable | Disables all of the interrupt levels at a particular interrupt priority and all interrupt levels at a less-favored interrupt priority. |
| i_enable | Enables all of the interrupt levels at a particular interrupt priority and all interrupt levels at a more-favored interrupt priority. |
The Memory Buffer (mbuf) kernel services provide functions to obtain, release, and manipulate memory buffers, or mbufs. These mbuf services provide the means to easily work with the mbuf data structure, which is defined in the /usr/include/sys/mbuf.h file. Data can be stored directly in an mbuf's data portion or in an attached external cluster. Mbufs can also be chained together by using the m_next field in the mbuf structure. This is particularly useful for communications protocols that need to add and remove protocol headers.
The Memory Buffer (mbuf) kernel services are:
| m_adj | Adjusts the size of an mbuf chain. |
| m_clattach | Allocates an mbuf structure and attaches an external cluster. |
| m_cat | Appends one mbuf chain to the end of another. |
| m_clgetm | Allocates and attaches an external buffer. |
| m_collapse | Guarantees that an mbuf chain contains no more than a given number of mbuf structures. |
| m_copydata | Copies data from an mbuf chain to a specified buffer. |
| m_copym | Creates a copy of all or part of a list of mbuf structures. |
| m_dereg | Deregisters expected mbuf structure usage. |
| m_free | Frees an mbuf structure and any associated external storage area. |
| m_freem | Frees an entire mbuf chain. |
| m_get | Allocates a memory buffer from the mbuf pool. |
| m_getclr | Allocates and zeros a memory buffer from the mbuf pool. |
| m_getclustm | Allocates an mbuf structure from the mbuf buffer pool and attaches a cluster of the specified size. |
| m_gethdr | Allocates a header memory buffer from the mbuf pool. |
| m_pullup | Adjusts an mbuf chain so that a given number of bytes is in contiguous memory in the data area of the head mbuf structure. |
| m_reg | Registers expected mbuf usage. |
In addition to the mbuf kernel services, the following macros are available for use with mbufs:
| m_clget | Allocates a page-sized mbuf structure cluster. |
| m_copy | Creates a copy of all or part of a list of mbuf structures. |
| m_getclust | Allocates an mbuf structure from the mbuf buffer pool and attaches a page-sized cluster. |
| M_HASCL | Determines if an mbuf structure has an attached cluster. |
| DTOM | Converts an address anywhere within an mbuf structure to the head of that mbuf structure. |
| MTOCL | Converts a pointer to an mbuf structure to a pointer to the head of an attached cluster. |
| MTOD | Converts a pointer to an mbuf structure to a pointer to the data stored in that mbuf structure. |
| M_XMEMD | Returns the address of an mbuf cross-memory descriptor. |
The operating system kernel provides several services for managing direct memory access DMA channels and performing DMA operations. Understanding DMA Transfers provides additional kernel services information.
| d_align | Assists in the allocation of DMA buffers. |
| d_cflush | Flushes the processor and I/O controller (IOCC) data caches when using the long term DMA_WRITE_ONLY mapping of direct memory access (DMA) buffers approach to the bus device DMA. |
| d_clear | Frees a DMA channel. |
| d_complete | Cleans up after a DMA transfer. |
| d_init | Initializes a DMA channel. |
| d_map_init | Allocates and initializes resources for performing DMA with PCI and ISA devices. |
| d_mask | Disables a DMA channel. |
| d_master | Initializes a block-mode DMA transfer for a DMA master. |
| d_move | Provides consistent access to system memory accessed asynchronously by a device and the processor on the system. |
| d_roundup | Assists in allocation of DMA buffers. |
| d_slave | Initializes a block-mode DMA transfer for a DMA slave. |
| d_unmask | Enables a DMA channel. |
Block I/O Buffer Cache Kernel Services Overview.