pwritev.c

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/*-------------------------------------------------------------------------
 *
 * pwritev.c
 *    Implementation of pwritev(2) for platforms that lack one.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/port/pwritev.c
 *
 * Note that this implementation changes the current file position, unlike
 * the POSIX-like function, so we use the name pg_pwritev().
 *
 *-------------------------------------------------------------------------
 */


#include "postgres.h"

#ifdef WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif

#include "port/pg_iovec.h"

ssize_t
pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
#ifdef HAVE_WRITEV
    if (iovcnt == 1)
        return pg_pwrite(fd, iov[0].iov_base, iov[0].iov_len, offset);
    if (lseek(fd, offset, SEEK_SET) < 0)
        return -1;
    return writev(fd, iov, iovcnt);
#else
    ssize_t     sum = 0;
    ssize_t     part;

    for (int i = 0; i < iovcnt; ++i)
    {
        part = pg_pwrite(fd, iov[i].iov_base, iov[i].iov_len, offset);
        if (part < 0)
        {
            if (i == 0)
                return -1;
            else
                return sum;
        }
        sum += part;
        offset += part;
        if (part < iov[i].iov_len)
            return sum;
    }
    return sum;
#endif
}