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BGETBF.C
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1989-08-30
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/* Copyright (c) 1989 Citadel */
/* All Rights Reserved */
/* #ident "bgetbf.c 1.1 - 89/07/03" */
#include <errno.h>
/* #include <string.h> */
#include "blkio_.h"
/*man---------------------------------------------------------------------------
NAME
bgetbf - get a block field from a block file
SYNOPSIS
#include <blkio.h>
int bgetbf(bp, bn, offset, buf, bufsize)
BLKFILE *bp;
bpos_t bn;
size_t offset;
void *buf;
size_t bufsize;
DESCRIPTION
The bgetbf function reads a field from block number bn in the block file
associated with BLKFILE pointer bp into buf. The field begins offset
characters from the beginning of the block and is bufsize characters
long. buf must point to a storage area at least bufsize characters long.
Block numbering starts at 1.
bgetbf will fail if one or more of the following is true:
[EINVAL] bp is not a valid BLKFILE pointer.
[EINVAL] bn or bufsize is less than 1.
[EINVAL] buf is the NULL pointer.
[BEBOUND] offset + bufsize extends beyond the boundary
of block bn.
[BEBOUND] End of file not on block boundary.
[BEEOF] There are not bn blocks in the file.
[BENOPEN] bp is not open for reading.
SEE ALSO
bgetb, bgethf, bputbf.
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned, and errno set to indicate the error.
------------------------------------------------------------------------------*/
int bgetbf(bp, bn, offset, buf, bufsize)
BLKFILE * bp;
bpos_t bn;
size_t offset;
void * buf;
size_t bufsize;
{
int rs = 0;
int i = 0;
size_t bufno = 0;
errno = 0;
/* validate arguments */
if (!b_valid(bp)) {
errno = EINVAL;
return -1;
}
if ((bn < 1) || (buf == NULL) || (bufsize < 1)) {
errno = EINVAL;
return -1;
}
/* check if not open for reading */
if (!(bp->flags & BIOREAD)) {
errno = BENOPEN;
return -1;
}
/* check if block boundary is crossed */
if ((offset + bufsize) > bp->blksize) {
errno = BEBOUND;
return -1;
}
/* check if not bn blocks in file */
if (bn >= bp->endblk) {
errno = BEEOF;
return -1;
}
/* check if not buffered */
if (bp->bufcnt == 0) {
rs = b_ugetf(bp, bn, offset, buf, bufsize);
if (rs == -1) {
BEPRINT;
return -1;
}
errno = 0;
return 0;
}
/* search buffer list for block */
for (i = 1; i <= bp->bufcnt; i++) {
if ((b_block_p(bp, (size_t)i)->bn == bn)
&& (b_block_p(bp, (size_t)i)->flags & BLKREAD)) {
bufno = i;
break;
}
}
/* if not found, use least recently used buffer */
if (bufno == 0) {
bufno = bp->least;
rs = b_put(bp, bufno); /* flush previous contents */
if (rs == -1) {
BEPRINT;
return -1;
}
b_block_p(bp, bufno)->flags = 0;
b_block_p(bp, bufno)->bn = bn;
/* read block from file */
rs = b_get(bp, bufno);
if (rs == -1) {
BEPRINT;
return -1;
}
}
/* copy from block buffer into buf */
memcpy(buf, (void *)((char *)b_blkbuf(bp, bufno) + offset), bufsize);
/* move block buffer bufno to most recently used end of list */
rs = b_mkmru(bp, bufno);
if (rs == -1) {
BEPRINT;
return -1;
}
errno = 0;
return 0;
}