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#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <stdio.h>
#include <unistd.h>
#include <stddef.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
int heat_the_cache(int fd)
{
char buf[1024];
int rv;
do {
retry_read:
rv = read(fd, buf, sizeof(buf));
if( -1 == rv
&& EINTR == errno ) {
goto retry_read;
}
} while( 0 < rv );
return rv != 0;
}
int main(int argc, char *argv[])
{
int i, fd_null, n_fileslocked;
fd_set phony_fdset;
char *buf;
if( 2 > argc ) {
fprintf(stderr,
"Usage:\n%s [filenames]\n",
argv[0] );
return 1;
}
n_fileslocked = 0;
for(i = 1; i < argc; ++i) {
char const * const filename = argv[i];
int fd;
struct stat st;
void *ptr;
retry_open:
fd = open(filename, O_RDONLY);
if( -1 == fd ) {
if( EINTR == errno ) {
goto retry_open;
} else
{
fprintf(stderr,
"error open('%s'): %s\n",
filename,
strerror(errno) );
continue;
}
}
if( -1 == fstat(fd, &st) ) {
fprintf(stderr,
"error fstat(fd['%s']): %s\n",
filename,
strerror(errno) );
goto finish_file;
}
ptr = mmap(
NULL,
st.st_size,
PROT_READ,
MAP_SHARED | MAP_LOCKED,
fd,
0 );
if( MAP_FAILED == ptr ) {
fprintf(stderr,
"error mmap(fd['%s'], 0..%lld): %s\n",
filename,
(long long)st.st_size,
strerror(errno) );
goto finish_file;
}
if( -1 == mlock(ptr, st.st_size) ) {
fprintf(stderr,
"error mlock(ptr[fd['%s']]=%p): %s\n",
filename,
ptr,
strerror(errno) );
goto finish_file;
}
++n_fileslocked;
heat_the_cache(fd);
finish_file:
close(fd);
}
if( !n_fileslocked ) {
return 1;
}
fprintf(stderr, "Files locked and cache heated up. Going to sleep, .zZ...\n");
/* At this point the program shall sleep until a terminating
* signal arrives. To do so a nice side effect of the definition
* of /dev/null behavior is used: read on a /dev/null fd always
* return 0, which correspond to EOF which is a "no content
* available for read (yet)" situation for which select waits.
* So by selecting for a read a fd on /dev/null we can put the
* process to sleep. */
fd_null = open("/dev/null", O_RDONLY);
if( -1 == fd_null ) {
fprintf(stderr,
"error open('/dev/null'): %s\n",
strerror(errno) );
return 1;
}
FD_ZERO(&phony_fdset);
FD_SET(fd_null, &phony_fdset);
if( -1 == select(fd_null, &phony_fdset, NULL, NULL, NULL) ) {
fprintf(stderr,
"error select(...): %s\n",
strerror(errno) );
return 1;
}
return 0;
}
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