77 lines
2.3 KiB
C
77 lines
2.3 KiB
C
/* Z%fifo.h 1.1 94/10/31 SMI; */
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/* Modification History:
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* M000:
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* Changed FIFOBSZ from 4096 to 4092. Note well that when FIFOBSZ is
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* equal to FIFOBUF, a union is used instead of a structure pointer.
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* under a heavy load, this causes a kernel panic (see escalation #917).
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*/
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#ifndef _specfs_fifo_h
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#define _specfs_fifo_h
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#ifdef KERNEL
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/*
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* Configuration Parameters
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*
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* These parameters are tuned by editing the system configuration file.
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* The following lines establish the default values.
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*/
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#ifndef FIFOCNT
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#define FIFOCNT 10 /* number of simultaneously open fifos */
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#endif
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/*
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* The following parameters are assumed not to require tuning.
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*/
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#define FIFOBUF 4096 /* max # bytes stored in a fifo */
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#define FIFOMAX ~0 /* largest size of a single write to a fifo */
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#define FIFOBSZ 4092 /* number of data bytes in each fifo data buffer *//*M000*/
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#define FIFOMNB (FIFOBUF*(FIFOCNT+1)) /* # bytes allowed for all fifos */
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/*
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* NOTE: When FIFOBUF == FIFOBSZ, a single buffer is used for each fifo.
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* Multiple, linked buffers will be used if FIFOBUF > FIFOBSZ.
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* In this case, FIFOBUF should be a multiple of FIFOBSZ and,
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* in order to minimize unnecessary fragmentation, FIFOBSZ should
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* probably be set to a power of 2 minus 4 (e.g., 4092).
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*
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* Note, also, that this decision is made at compile-time so
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* the run-time modification of fifoinfo parameters is dangerous.
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*/
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#if (FIFOBUF > FIFOBSZ)
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struct fifo_bufhdr {
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struct fifo_bufhdr *fb_next; /* ptr to next buffer */
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char fb_data[1];
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};
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#define FIFO_BUFHDR_SIZE (sizeof (struct fifo_bufhdr *))
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#define FIFO_BUFFER_SIZE (fifoinfo.fifobsz + FIFO_BUFHDR_SIZE)
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/* M000: avoid this like the plague! */
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#else /*(FIFOBUF == FIFOBSZ)*/
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struct fifo_bufhdr {
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union {
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struct fifo_bufhdr *fu_next;
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char fu_data[1]; /* must be at first byte in buffer */
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} fb_u;
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};
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#define fb_next fb_u.fu_next
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#define fb_data fb_u.fu_data
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#define FIFO_BUFFER_SIZE (fifoinfo.fifobsz)
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#endif
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/*
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* Fifo information structure.
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*/
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struct fifoinfo {
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int fifobuf, /* max # bytes stored in a fifo */
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fifomax, /* largest size of a single write to a fifo */
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fifobsz, /* # of data bytes in each fifo data buffer */
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fifomnb; /* max # bytes reserved for all fifos */
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};
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int fifo_alloc; /* total number of bytes reserved for fifos */
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struct fifoinfo fifoinfo; /* fifo parameters */
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#endif KERNEL
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#endif /*!_specfs_fifo_h*/
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