ESP32-S3 Posix FILE SYSTEM APIs crashing regardless LIBC implementation

[alespitfire]

Hello,
I am trying without any success to have POSIX library working with file system API.
In particular I need fopen, fread, fwrite and fstat.
I am working with the ESP32-S3 as mcu connected to an SD card.
I have no constraints about Zephyr version. I have no constraints about file system (but a preference for FATFS).

I have tried to readjust the fs_sample to use the posix functions to read from files but I fail, the system crashes.
(look at the attached file main.c function void test_posix(const char *path) L.125)

fs_sample.zip

I suspect the issue is in the libc or posix implementation as the fs_sample based on Zephyr File System works flawlessly.
In addition without expliciting which libc the compiler should use, the system does not crash; instead by adding CONFIG_NEWLIB_LIBC=y or CONFIG_PICOLIBC_USE_MODULE=y the system crashes.

Can you help me to figure this out?

Thank you

[sylvioalves]

@alespitfire will check.

[wmrsouza]

@alespitfire Using your modified version of fs_sample, I reproduced the behavior you described and confirmed that the failure occurs when the fread() function is called.

issue #66940 - libc: implement fread() was closed indicating that the implementation of fread() in Zephyr is not currently planned, therefore, fread() is probably not working on other platforms besides Espressif either.

As a workaround, I replaced the fopen() and fread() calls with calls to open() and read() in your modified version of fs_sample - along with the necessary additional changes - and I can confirm that open() and read() are working in Zephyr:

#include <unistd.h>
#include <fcntl.h>

static void test_posix(const char *path)
{
	char fname[MAX_PATH];
	snprintk(fname, sizeof(fname), "%s/%s", path, SOME_FILE_NAME);

	// FILE *fp = fopen(fname, "r");
	// if (fp == NULL) {
	int fd = open(fname, O_RDONLY);
	if (fd < 0) {
		printk("File %s open error\n", fname);
		return;
	}

	char read_buf[26];
	memset(read_buf, 0, sizeof(read_buf));

	// size_t n = fread(read_buf, 1, sizeof(read_buf), fp);
	// if (n > 0) {
	// 	printk("Read %zu bytes from %s: '%s'\n", n, fname, read_buf);
	// } else if (n >= sizeof("Hello World!")) {
	// 	printk("Read buffer too small from %s\n", fname);
	// } else {
	// 	printk("Read error or zero bytes read from %s\n", fname);
	// }
	size_t n = read(fd, read_buf, sizeof(read_buf));
	if (n > 0) {
		read_buf[n] = '\0';
		printk("Read %zu bytes from %s: '%s'\n", n, fname, read_buf);
	} else {
		printk("Read error or zero bytes read from %s\n", fname);
	}
}