determine if a file/folder resides on a ssd or rotating media

ssd.cpp

#include <cstdio>
#include <string>
#include <vector>
#include <algorithm>
#include <cstring>
#include <iostream>
#include <mntent.h>
#include <limits.h>

struct MountPointEntity {
	struct mntent me;
	char buff[PATH_MAX * 3];
};

std::vector<MountPointEntity*> getMountPoints() {
	// /etc/mtab contains a list of all mounted devices
	FILE* mf = setmntent("/etc/mtab", "r");
	if ( mf == nullptr )
		return {};


	// iterate over entries adding them to a database
	std::vector<MountPointEntity*> ret;
	for ( ;; )
	{
		auto* ent = new MountPointEntity;	
		if ( getmntent_r( mf, &ent->me, ent->buff, PATH_MAX * 3 ) == nullptr ) 
		{
			delete ent;
			break;
		}
		ret.push_back(ent);		
	}

	// Want longer dir names first since they could be subpaths
	std::sort(ret.begin(), ret.end(), [](MountPointEntity* a, MountPointEntity* b) {
		return strlen(a->me.mnt_dir) > strlen(b->me.mnt_dir);
	});
	return ret;	
}

bool isOnSSD(char* path) {
	char p[PATH_MAX];
	if ( realpath(path, p) == nullptr )
		return false;
	
	static auto mps = getMountPoints();
	struct mntent* me = nullptr;
	for (auto* mp : mps) {
		if ( strncmp( mp->me.mnt_dir, p, strlen( mp->me.mnt_dir ) ) == 0 ) {
			me = &mp->me;
			printf("match: %s -- %s\n", mp->me.mnt_dir, p); 
			break;
		}
	}
	if ( me == nullptr ) {
		puts("not found");
		return false;
	}
	printf("dev: %s\n", me->mnt_fsname);
	if ( strncmp( "/dev/", me->mnt_fsname, 5 ) == 0 )
		me->mnt_fsname += 5;
	std::string sysfpath = "/sys/class/block/";
	sysfpath += me->mnt_fsname;
	sysfpath += "/queue/rotational";
	FILE* f = fopen(sysfpath.c_str(), "r");
	if ( f == nullptr ) {
		puts(me->mnt_fsname);
		puts("not in sysfs");
		sysfpath = "/sys/class/block/";
		sysfpath += me->mnt_fsname;
		sysfpath += "/../queue/rotational";
		f = fopen(sysfpath.c_str(), "r");
		if ( f == nullptr ) {
			puts(me->mnt_fsname);
			puts("not in sysfs");
			return false;
		}
	}
	const char c = fgetc(f);
	printf("rot: %c\n", c);
	return c == '0';

	// Other method that doesn't always work
/*
	struct mntent minfo;
	if ( getmntent_r(mf, &minfo) == nullptr ) {
		endmntent(mf);
		return false;  
	}
	endmntent(mf);
	std::cout <<minfo.mnt_fsname <<std::endl;

	struct statvfs statinfo;
	statvfs(path, &statinfo);

	// The bitshift trick works experimentally but not documented anywhere
	std::cout <<statinfo.f_fsid <<std::endl;
	const int devid = (*((int*)&statinfo.f_fsid)) >> 8;

	std::string sysfpath = "/sys/dev/block/" + std::to_string(devid) + ":0/queue/rotational";
	FILE* f = fopen(sysfpath.c_str(), "r");
	if ( f == nullptr )
		return false;
	const char c = fgetc(f);
	fclose(f);
	return c == '0';
*/
}

int main(int argc, char** argv) {
	if ( isOnSSD( argv[1] ) )
		std::cout <<"SSD\n";
	else
		std::cout <<"Disk\n";
}