Re: [PATCH 2/2] mkfs.f2fs: make the default extensions list much more sensical

[Ju Hyung Park <qkrwngud825@gmail.com>]

Hi Chao,

On Wed, Apr 17, 2019 at 6:41 PM Chao Yu <yuchao0@huawei.com> wrote:
> Actually, kernel will compare each character of extension in list with file's
> extension, rather than prefix, could you confirm that? :)

Just wrote a sample C program with namei.c's is_extension_exist() to
confirm this indeed works as intended.

Output:
Checking against "jp"
jpg: false
abc.jpg: true
abc.jpeg: true
abc.jpg.tmp: true
abc.jpeg.tmp: true
abc.jgp: false

Source:

#include <stdio.h>
#include <stddef.h>
#include <string.h>

static int is_extension_exist(const unsigned char *s, const char *sub)
{
    size_t slen = strlen(s);
    size_t sublen = strlen(sub);
    int i;

    /*
     * filename format of multimedia file should be defined as:
     * "filename + '.' + extension + (optional: '.' + temp extension)".
     */
    if (slen < sublen + 2)
        return 0;

    for (i = 1; i < slen - sublen; i++) {
        if (s[i] != '.')
            continue;
        if (!strncasecmp(s + i + 1, sub, sublen))
            return 1;
    }

    return 0;
}

static const char *list[] = {
    "jpg",
    "abc.jpg",
    "abc.jpeg",
    "abc.jpg.tmp",
    "abc.jpeg.tmp",
    "abc.jgp",
    NULL
};

#define CHECK "jp"

int main() {
    printf("Checking against \"%s\"\n", CHECK);

    for (int i = 0; list[i]; i++) {
        if (is_extension_exist(list[i], CHECK))
            printf("%s: true\n", list[i]);
        else
            printf("%s: false\n", list[i]);
    }
}