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sortix--sortix/libc/ioleast/preadleast.cpp
2015-02-08 22:58:32 +01:00

49 lines
1.6 KiB
C++

/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2012, 2013, 2015.
This file is part of the Sortix C Library.
The Sortix C Library is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
The Sortix C Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
ioleast/preadleast.cpp
Reads at least as much data as requested or more from the given offset.
*******************************************************************************/
#include <assert.h>
#include <errno.h>
#include <ioleast.h>
#include <stdint.h>
#include <unistd.h>
extern "C"
size_t preadleast(int fd, void* buf_ptr, size_t least, size_t max, off_t off)
{
assert(least <= max);
unsigned char* buf = (unsigned char*) buf_ptr;
size_t done = 0;
do
{
ssize_t amount = pread(fd, buf + done, max - done, off + done);
if ( amount < 0 )
return done;
if ( !amount && done < least )
return errno = EEOF, done;
if ( !amount )
break;
done += amount;
} while ( done < least );
return done;
}