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#define _GNU_SOURCE
#include <sys/mman.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
char buf[128*1024];
int main(int argc, char *argv[])
{
if( 2 > argc ){
fprintf(stderr,
"Read stdin into a memfd reservoir file and use this as stdin for a subsequently executed command.\n"
"usage: %s <command and argument>\n",
(argc ? argv[0] : "rsvr") );
return EXIT_FAILURE;
}
int rsvr_fd = memfd_create("reservoiur", MFD_CLOEXEC);
if( 0 > rsvr_fd ){
perror("memfd_create('reservoiur', MFD_CLOEXEC)");
return EXIT_FAILURE;
}
ssize_t rb = 0, wb = 0;
do {
rb = read(0, buf, sizeof(buf));
if( 0 >= rb ){ continue; }
for( ssize_t cb = 0
; 0 <= wb && (cb < rb)
; cb += ((0 < wb) ? wb : 0)
){
wb = write(rsvr_fd, (buf+cb), (rb-cb));
if( (0 > wb) && (EINTR == errno) ){ wb = 0; }
}
} while( (0 < rb)
|| (0 > rb) && EINTR == errno );
if( 0 > rb ){ perror("read(stdin)"); }
if( 0 > wb ){ perror("write(reservoir)"); }
if( 0 > rb || 0 > wb ){ return EXIT_FAILURE; }
if( 0 > dup2(rsvr_fd, 0) ){
perror("dup2(reservoir, stdin)");
return EXIT_FAILURE;
}
close(rsvr_fd);
memmove(argv, argv+1, sizeof(*argv)*(argc-1));
argv[argc-1] = NULL;
if( 0 > execvp(argv[0], argv) ){
perror("exec(...)");
}
return EXIT_FAILURE;
}
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