Frequency count: hard mode.

accum.sh

#!/bin/zsh

# Find each struct's usage frequency in each subsystem. In each search, discard
# the files that have no matches, get rid of the directory prefix, only keep
# the subsystem, and then pipe the information out to a temporary file. Loop
# through every (Subsystem Of File, Count) tuple and sum up the contribution
# from each subsystem to that struct's frequency.

for line in $(cat structs.txt); do
	echo ">"$line
	grep -rEoIc "struct\s+""$(echo $line | cut -d : -f 2)" /mnt/ram/linux | grep -v ':0$' | sed 's|/mnt/ram/linux/||g' | sed -r "s|/(.*):|:|g" > /mnt/ram/struct
	./reduce
done

reduce.cc

#include <map>                       
 
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <string>

using namespace std;

int main()
{
    int fd = open("/mnt/ram/struct", O_RDWR);
    if (fd < 0) {
        perror("open");
        return 1;
    }

    struct stat st;
    if (fstat(fd, &st) < 0) {
        perror("fstat");
        return 1;
    }

    char *mem = (char *) mmap(0, st.st_size, PROT_READ | PROT_WRITE,
            MAP_SHARED /* Don't allocate new pages when we poke in NULLs;
                          anyway this gets flushed to a ramfs. */
            fd, 0);
    if (mem == (char *) MAP_FAILED) {
        perror("mmap");
        return 1;
    }

    map<string, int> freq;
    char *cur = mem;
    char *end = mem + st.st_size;
    while (cur < end) {
        char *colon = (char *) rawmemchr(cur, ':');
        *colon = '\0';

        // subsystem
        string key = string((const char *) cur);

        cur = (char *) rawmemchr(colon + 2, '\n');
        *cur = '\0';

        // frequency count
        int val = atoi(colon + 1);

        if (freq.count(key)) {
            freq[key] += val;
        } else {
            freq.emplace(key, val);
        }

        ++cur;
    }
    
    for (auto it = freq.begin(); it != freq.end(); ++it) {
        printf("%s:%d\n", it->first.c_str(), it->second);
    }

    return 0;
}