Implementation of df Command in shell for Android System
- 2021-10-27 08:51:45
- OfStack
When we hit the command df in shell, we will see:
root@android:/ # df
Filesystem Size Used Free Blksize
/dev 446.8M 36.0K 446.8M 4096
/mnt/secure 446.8M 0.0 K 446.8M 4096
/mnt/asec 446.8M 0.0 K 446.8M 4096
/mnt/cart0 446.8M 0.0 K 446.8M 4096
/mnt/obb 446.8M 0.0 K 446.8M 4096
/system 1.5 G 376.6M 1.1 G 1024
/data 5.2 G 188.9M 5.0 G 4096
/cache 124.0M 16.1M 107.9M 4096
/mnt/.cci 503.9M 16.4M 487.6M 4096
/storage/sdcard0 5.2 G 188.9M 5.0 G 4096
/mnt/external_sd 7.5 G 475.0M 7.0 G 4096
So, how did this come about?
In fact, it is very simple, that is, using statfs this function to query the information related to the file system, and then enumerate it in turn.
If you use this function?
See below:
http://baike.baidu.com/link?url=EVV8n-l-DXfgNwYj5Lqzo0HFvYaXMYEzTBMVtuyrq0QCvpaD0Lr0RjX81L6jTE6RXplNC_cNec8tgdsDleX2pq
So how is df implemented? See source code df. c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/statfs.h>
static int ok = EXIT_SUCCESS;
// Calculates based on the size of the mounted file
static void printsize(long double n)
{
char unit = 'K';
n /= 1024;
if (n > 1024) {
n /= 1024;
unit = 'M';
}
if (n > 1024) {
n /= 1024;
unit = 'G';
}
printf("%-4.1Lf%c", n, unit);
}
static void df(char *s, int always) {
//
struct statfs st;
//statfs Function can be used to query information about the file system.
if (statfs(s, &st) < 0) {
fprintf(stderr, "%s: %s\n", s, strerror(errno));
ok = EXIT_FAILURE;
} else {
if (st.f_blocks == 0 && !always)
return;
printf("%-20s ", s);
printsize((long double)st.f_blocks * (long double)st.f_bsize);
printf(" ");
printsize((long double)(st.f_blocks - (long double)st.f_bfree) * st.f_bsize);
printf(" ");
printsize((long double)st.f_bfree * (long double)st.f_bsize);
printf(" %d\n", (int) st.f_bsize);
}
}
int df_main(int argc, char *argv[]) {
printf("Filesystem Size Used Free Blksize\n");
if (argc == 1) {
char s[2000];
// The mounted files are all in the /proc/mounts Display below
FILE *f = fopen("/proc/mounts", "r");
while (fgets(s, 2000, f)) {
char *c, *e = s;
for (c = s; *c; c++) {
if (*c == ' ') {
e = c + 1;
break;
}
}
for (c = e; *c; c++) {
if (*c == ' ') {
*c = '\0';
break;
}
}
df(e, 0);
}
fclose(f);
} else {
int i;
for (i = 1; i < argc; i++) {
df(argv[i], 1);
}
}
exit(ok);
}
Summarize