add file flush in sys_close and sys_exit

[lhw2002426]

No description provided.

[coolyjg]

Please fix bugs and some code.

[coolyjg]

I think there are concurrency bugs for the sys_exit and sys_pthread_exit:
Checking fd_table_count() in every while loop seems to be unsafe for multi-thread situation..... I'll take more consideration..... @ken4647
By the way, ramfs should implement a fake flush as well.

[coolyjg]

Use debug

[coolyjg]

Use debug

[coolyjg]

Unused?

[coolyjg]

For example:
If thread A exit, two files are opened with fd=3, fd=4.
FIRST loop: flush fd=3, get fd_table_count=2, now_fd_count=1
SECOND loop: flush fd=4
(thread B open another file fd=5, then fd_table_count -> 3)
get fd_table_count=3, now_fd_count=2, continue loop.
THIRD loop: flush fd=5
(thread B now close fd=5, then fd_table_count -> 2)
get fd_table_count=2, now_fd_count=3, still continue loop. And loop for 1024 times which caused
very bad performance.
This example might be too extreme, but I think the situation is not rare. @ken4647
There are some of my thoughts:

• sync operation should always be idempotent(need to check current implementation).
• A big fd_table lock when exiting. (I think it's unacceptable)
• Gather all opened fd one time when exiting.

[coolyjg]

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <pthread.h>


char* setFileName(char* s, int i){
    s[4] = i + '0';
    return s;
}


void* threadA(void* _args){
    char* s = (char*)malloc(sizeof(char)*6);
    strcpy(s, "file0");
    s[5] = '\0';

    for(int i = 0; i<10; i++) {
        s = setFileName(s, i);
        int fd = open(s, O_RDWR | O_CREAT);
        printf("fd = %d, name: %s\n", fd, s);
        close(fd);
    }
}

void* threadB(void* _args){
    char* s = (char*)malloc(sizeof(char)*6);
    strcpy(s, "Fale0");
    s[5] = '\0';

    for(int i = 0; i<3; i++) {
        s = setFileName(s, i);
        int fd = open(s, O_RDWR | O_CREAT);
        printf("fd = %d, name: %s\n", fd, s);
    }
}


int main()
{
    pthread_t p1, p2;
    pthread_create(&p1, NULL, threadA, NULL);
    pthread_create(&p2, NULL, threadB, NULL);
    pthread_join(p1, NULL);
    pthread_join(p2, NULL);

    return 0;
}

make A=apps/c/helloworld/ MUSL=y FEATURES=fs,multitask,blkfs,fd BLK=y LOG=debug ARCH=aarch64 run SMP=4

[coolyjg]

I think this PR should be merged after #81 is fixed.

[coolyjg]

In rust-fatfs, when closing file, files would be called flush automatically, in rust-fats/src/file.rs line 235