The previous answer is correct -- mkfifo() just calls mknod() to create a special file, and FAT32 doesn't support that.
As an alternative you may want to consider using Linux's "abstract namespace" UNIX-domain sockets. They should be roughly equivalent to a named pipe. You can access them by name, but they're not part of the filesystem, so you don't have to deal with various permission issues. Note the socket is bi-directional.
Since it's a socket, you may need INTERNET permission. Not sure about that.
Here's a quick bit of client/server sample code:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stddef.h>
#include <sys/socket.h>
#include <sys/un.h>
/*
* Create a UNIX-domain socket address in the Linux "abstract namespace".
*
* The socket code doesn't require null termination on the filename, but
* we do it anyway so string functions work.
*/
int makeAddr(const char* name, struct sockaddr_un* pAddr, socklen_t* pSockLen)
{
int nameLen = strlen(name);
if (nameLen >= (int) sizeof(pAddr->sun_path) -1) /* too long? */
return -1;
pAddr->sun_path[0] = '\0'; /* abstract namespace */
strcpy(pAddr->sun_path+1, name);
pAddr->sun_family = AF_LOCAL;
*pSockLen = 1 + nameLen + offsetof(struct sockaddr_un, sun_path);
return 0;
}
int main(int argc, char** argv)
{
static const char* message = "hello, world!";
struct sockaddr_un sockAddr;
socklen_t sockLen;
int result = 1;
if (argc != 2 || (argv[1][0] != 'c' && argv[1][0] != 's')) {
printf("Usage: {c|s}\n");
return 2;
}
if (makeAddr("com.whoever.xfer", &sockAddr, &sockLen) < 0)
return 1;
int fd = socket(AF_LOCAL, SOCK_STREAM, PF_UNIX);
if (fd < 0) {
perror("client socket()");
return 1;
}
if (argv[1][0] == 'c') {
printf("CLIENT %s\n", sockAddr.sun_path+1);
if (connect(fd, (const struct sockaddr*) &sockAddr, sockLen) < 0) {
perror("client connect()");
goto bail;
}
if (write(fd, message, strlen(message)+1) < 0) {
perror("client write()");
goto bail;
}
} else if (argv[1][0] == 's') {
printf("SERVER %s\n", sockAddr.sun_path+1);
if (bind(fd, (const struct sockaddr*) &sockAddr, sockLen) < 0) {
perror("server bind()");
goto bail;
}
if (listen(fd, 5) < 0) {
perror("server listen()");
goto bail;
}
int clientSock = accept(fd, NULL, NULL);
if (clientSock < 0) {
perror("server accept");
goto bail;
}
char buf[64];
int count = read(clientSock, buf, sizeof(buf));
close(clientSock);
if (count < 0) {
perror("server read");
goto bail;
}
printf("GOT: '%s'\n", buf);
}
result = 0;
bail:
close(fd);
return result;
}