Fail allocate but print success?

[Userzxcvbvnm]

Subject of the issue

In this situation, wamr fails to allocate space which is expected ,however, wamr prints success.

Test case

The test case is:

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

void print_file_size(int fd){
    struct stat st;
    if (fstat(fd, &st) == -1) {
        printf("Get file size failed.\n");
    } else {
        printf("Get file size: %ld bytes.\n", st.st_size);
    }
}

int get_fd(const char *filename, int flags) {
    int fd = open(filename, flags);

    if (fd == -1) {
        printf("Get file descriptor of file %s failed!\n", filename);
        return -1;
    } else {
        printf("Get file descriptor of file %s succeed!\n", filename);
        return fd;
    }
}

void closebyfd(int fd) {
    if (close(fd) == -1) {
        printf("Close the file by descriptor failed!\n");
    }
}

void fd_allocate_00085_gxX49(int fd) {
    printf("Enter function fd_allocate_00085_gxX49\n");

    int result = posix_fallocate(fd, 1, 7);

    if (result == 0) {
        printf("Space allocation in file successful.\n");
    } else {
        printf("Error allocating space in file.\n");
    }
}

int main() {
    int fd = get_fd("subdir_2/subfile_1", O_WRONLY | O_APPEND);
    if (fd == -1) {
        return -1; // Return from main if get_fd failed
    }

    print_file_size(fd);
    fd_allocate_00085_gxX49(fd);
    print_file_size(fd);

    closebyfd(fd);

    return 0;
}

Your environment

Ubuntu 20.04 x86_64 WAMR 1.3.2 and WAMR 1.2.3

Steps to reproduce

(1)compile to wasm:./wasi-sdk-21.0/bin/clang --target=wasm32-unkown-wasi --sysroot=./wasi-sdk-21.0/share/wasi-sysroot test.c -o test.wasm

(2)Running wasm: (Before run the Wasm file, file subdir_2/subfile_1 exists, and file size is 26.) iwasm --dir=. test.wasm

Expected behavior

prints:

Get file descriptor of file subdir_2/subfile_1 succeed!
Get file size: 26 bytes.
Enter function fd_allocate_00085_gxX49
Error allocating space in file.
Get file size: 26 bytes.

This is what wasmtime does.

Actual behavior

WAMR prints:

Get file descriptor of file subdir_2/subfile_1 succeed!
Get file size: 26 bytes.
Enter function fd_allocate_00085_gxX49
Space allocation in file successful.
Get file size: 26 bytes.

Extra Info

Anything else you'd like to add?

[lum1n0us]

IIUC, you have two questions:

1. why wasmtime failed but wamr pass
2. why wamr says "Space allocation in file successful." but the before and after file size are same.

I am just going to answer the second one 😄 .

According to manual,

The function posix_fallocate() ensures that disk space is allocated for the file referred to by the file descriptor fd for the bytes. ... If the size of the file is less than offset+len, then the file is increased to this size; otherwise the file size is left unchanged.

It is not going to increase the file size if there is enough space. In this case, the file size is 26, and offset+len is 7. So, the file size is left unchanged.

And for sure, you'll see a file size change if use a bigger len, like int result = posix_fallocate(fd, 1, 70);

[yamt]

why wasmtime failed but wamr pass

because wasmtime has deprecated fd_allocate while ago, it always fails.

this doesn't seem like a bug in wamr.