59 lines
1.2 KiB
C
59 lines
1.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* preadv.c
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* Implementation of preadv(2) for platforms that lack one.
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*
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* Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* src/port/preadv.c
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*
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* Note that this implementation changes the current file position, unlike
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* the POSIX-like function, so we use the name pg_preadv().
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#ifdef WIN32
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#include <windows.h>
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#else
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#include <unistd.h>
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#endif
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#include "port/pg_iovec.h"
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ssize_t
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pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
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{
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#ifdef HAVE_READV
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if (iovcnt == 1)
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return pread(fd, iov[0].iov_base, iov[0].iov_len, offset);
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if (lseek(fd, offset, SEEK_SET) < 0)
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return -1;
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return readv(fd, iov, iovcnt);
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#else
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ssize_t sum = 0;
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ssize_t part;
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for (int i = 0; i < iovcnt; ++i)
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{
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part = pread(fd, iov[i].iov_base, iov[i].iov_len, offset);
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if (part < 0)
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{
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if (i == 0)
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return -1;
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else
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return sum;
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}
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sum += part;
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offset += part;
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if (part < iov[i].iov_len)
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return sum;
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}
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return sum;
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#endif
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}
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