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Provide pg_preadv() and pg_pwritev().

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Provide synchronous vectored file I/O routines.  These map to preadv()
and pwritev(), with fallback implementations for systems that don't have
them.  Also provide a wrapper pg_pwritev_with_retry() that automatically
retries on short writes.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKGJA%2Bu-220VONeoREBXJ9P3S94Y7J%2BkqCnTYmahvZJwM%3Dg%40mail.gmail.com
This commit is contained in:
Thomas Munro
2021-01-11 14:37:13 +13:00
parent 01334c92fa
commit 13a021f3e8
9 changed files with 238 additions and 34 deletions
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43
src/port/pread.c
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@@ -1,7 +1,7 @@
/*-------------------------------------------------------------------------
*
* pread.c
* Implementation of pread(2) for platforms that lack one.
* Implementation of pread[v](2) for platforms that lack one.
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
*
@@ -9,7 +9,8 @@
* src/port/pread.c
*
* Note that this implementation changes the current file position, unlike
* the POSIX function, so we use the name pg_pread().
* the POSIX function, so we use the name pg_pread(). Likewise for the
* iovec version.
*
*-------------------------------------------------------------------------
*/
@@ -23,6 +24,9 @@
#include <unistd.h>
#endif
#include "port/pg_iovec.h"
#ifndef HAVE_PREAD
ssize_t
pg_pread(int fd, void *buf, size_t size, off_t offset)
{
@@ -56,3 +60,38 @@ pg_pread(int fd, void *buf, size_t size, off_t offset)
return read(fd, buf, size);
#endif
}
#endif
#ifndef HAVE_PREADV
ssize_t
pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
#ifdef HAVE_READV
if (iovcnt == 1)
return pg_pread(fd, iov[0].iov_base, iov[0].iov_len, offset);
if (lseek(fd, offset, SEEK_SET) < 0)
return -1;
return readv(fd, iov, iovcnt);
#else
ssize_t sum = 0;
ssize_t part;
for (int i = 0; i < iovcnt; ++i)
{
part = pg_pread(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
}
#endif