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Provide pg_pread() and pg_pwrite() for random I/O.
Forward to POSIX pread() and pwrite(), or emulate them if unavailable. The emulation is not perfect as the file position is changed, so we'll put pg_ prefixes on the names to minimize the risk of confusion in future patches that might inadvertently try to mix pread() and read() on the same file descriptor. Author: Thomas Munro Reviewed-by: Tom Lane, Jesper Pedersen Discussion: https://postgr.es/m/CAEepm=02rapCpPR3ZGF2vW=SBHSdFYO_bz_f-wwWJonmA3APgw@mail.gmail.com
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‎configure

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@@ -15539,6 +15539,32 @@ esac
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fi
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ac_fn_c_check_func "$LINENO" "pread" "ac_cv_func_pread"
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if test "x$ac_cv_func_pread" = xyes; then :
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$as_echo "#define HAVE_PREAD 1" >>confdefs.h
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else
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case " $LIBOBJS " in
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*" pread.$ac_objext "* ) ;;
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*) LIBOBJS="$LIBOBJS pread.$ac_objext"
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;;
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esac
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fi
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ac_fn_c_check_func "$LINENO" "pwrite" "ac_cv_func_pwrite"
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if test "x$ac_cv_func_pwrite" = xyes; then :
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$as_echo "#define HAVE_PWRITE 1" >>confdefs.h
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else
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case " $LIBOBJS " in
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*" pwrite.$ac_objext "* ) ;;
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*) LIBOBJS="$LIBOBJS pwrite.$ac_objext"
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;;
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esac
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fi
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ac_fn_c_check_func "$LINENO" "random" "ac_cv_func_random"
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if test "x$ac_cv_func_random" = xyes; then :
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$as_echo "#define HAVE_RANDOM 1" >>confdefs.h

‎configure.in

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@@ -1698,6 +1698,8 @@ AC_REPLACE_FUNCS(m4_normalize([
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getrusage
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inet_aton
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mkdtemp
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pread
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pwrite
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random
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rint
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srandom

‎src/include/pg_config.h.in

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@@ -438,6 +438,9 @@
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/* Define to 1 if you have the `ppoll' function. */
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#undef HAVE_PPOLL
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/* Define to 1 if you have the `pread' function. */
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#undef HAVE_PREAD
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/* Define to 1 if you have the `pstat' function. */
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#undef HAVE_PSTAT
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@@ -453,6 +456,9 @@
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/* Have PTHREAD_PRIO_INHERIT. */
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#undef HAVE_PTHREAD_PRIO_INHERIT
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/* Define to 1 if you have the `pwrite' function. */
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#undef HAVE_PWRITE
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/* Define to 1 if you have the `random' function. */
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#undef HAVE_RANDOM
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‎src/include/pg_config.h.win32

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@@ -322,12 +322,18 @@
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/* Define to 1 if you have the `ppoll' function. */
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/* #undef HAVE_PPOLL */
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/* Define to 1 if you have the `pread' function. */
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/* #undef HAVE_PREAD */
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/* Define to 1 if you have the `pstat' function. */
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/* #undef HAVE_PSTAT */
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/* Define to 1 if the PS_STRINGS thing exists. */
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/* #undef HAVE_PS_STRINGS */
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/* Define to 1 if you have the `pwrite' function. */
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/* #undef HAVE_PWRITE */
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/* Define to 1 if you have the `random' function. */
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/* #undef HAVE_RANDOM */
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‎src/include/port.h

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@@ -392,6 +392,23 @@ extern double rint(double x);
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extern int inet_aton(const char *cp, struct in_addr *addr);
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#endif
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/*
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* Windows and older Unix don't have pread(2) and pwrite(2). We have
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* replacement functions, but they have slightly different semantics so we'll
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* use a name with a pg_ prefix to avoid confusion.
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*/
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#ifdef HAVE_PREAD
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#define pg_pread pread
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#else
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extern ssize_t pg_pread(int fd, void *buf, size_t nbyte, off_t offset);
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#endif
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#ifdef HAVE_PWRITE
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#define pg_pwrite pwrite
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#else
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extern ssize_t pg_pwrite(int fd, const void *buf, size_t nbyte, off_t offset);
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#endif
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#if !HAVE_DECL_STRLCAT
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extern size_t strlcat(char *dst, const char *src, size_t siz);
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#endif

‎src/port/pread.c

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/*-------------------------------------------------------------------------
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*
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* pread.c
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* Implementation of pread(2) for platforms that lack one.
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*
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* Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* src/port/pread.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 function, so we use the name pg_pread().
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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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ssize_t
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pg_pread(int fd, void *buf, size_t size, off_t offset)
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{
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#ifdef WIN32
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OVERLAPPED overlapped = {0};
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HANDLE handle;
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DWORD result;
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handle = (HANDLE) _get_osfhandle(fd);
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if (handle == INVALID_HANDLE_VALUE)
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{
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errno = EBADF;
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return -1;
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}
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overlapped.Offset = offset;
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if (!ReadFile(handle, buf, size, &result, &overlapped))
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{
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_dosmaperr(GetLastError());
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return -1;
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}
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return result;
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#else
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if (lseek(fd, offset, SEEK_SET) < 0)
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return -1;
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return read(fd, buf, size);
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#endif
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}

‎src/port/pwrite.c

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@@ -0,0 +1,55 @@
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/*-------------------------------------------------------------------------
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*
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* pwrite.c
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* Implementation of pwrite(2) for platforms that lack one.
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*
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* Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* src/port/pwrite.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 function, so we use the name pg_write().
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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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ssize_t
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pg_pwrite(int fd, const void *buf, size_t size, off_t offset)
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{
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#ifdef WIN32
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OVERLAPPED overlapped = {0};
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HANDLE handle;
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DWORD result;
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handle = (HANDLE) _get_osfhandle(fd);
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if (handle == INVALID_HANDLE_VALUE)
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{
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errno = EBADF;
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return -1;
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}
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overlapped.Offset = offset;
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if (!WriteFile(handle, buf, size, &result, &overlapped))
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{
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_dosmaperr(GetLastError());
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return -1;
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}
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return result;
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#else
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if (lseek(fd, offset, SEEK_SET) < 0)
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return -1;
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return write(fd, buf, size);
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#endif
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}

‎src/tools/msvc/Mkvcbuild.pm

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@@ -97,6 +97,7 @@ sub mkvcbuild
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srandom.c getaddrinfo.c gettimeofday.c inet_net_ntop.c kill.c open.c
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erand48.c snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c
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dirent.c dlopen.c getopt.c getopt_long.c
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pread.c pwrite.c
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pg_strong_random.c pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c
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pqsignal.c mkdtemp.c qsort.c qsort_arg.c quotes.c system.c
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sprompt.c strerror.c tar.c thread.c

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