isabella232 / libresource

CGroup aware resource querying library

libresource

library of interfaces through which we can get system resource information like memory, CPU, stat, networking, device etc. Currently most of such information is read from /proc and /sys.

Use case:

1: Ease of use - Currently applications and tools need to read this info mostly from /proc and /sys file-systems. In most of the cases complex string parsing is involved which is needed to be done in application code. With the library interfaces application can get the information directly and all the string parsing, if any, will be done by library.

2: Stability - If the format in which the information is provided in /proc or /sys file-system is changed then the application code is changed to align with those changes. Also if a better way to get information comes in future, like through a syscall or a sysconf then again application code needs to be changed to get the benefit of it. Library will take care of such changes.

3: Virtualization - In cases where DB is running in a virtualized environment using cgroup or namespaces, reading from /proc and /sys file-systems might not give correct information as these are not cgroup aware. Library API will take care of this e.g. if a process is running in a cgroup then library should provide information which is local to that cgroup.

Interfaces:

1: Resource id

Each resource is identified by a resource id. User land application should provide the id while calling the interfaces to fetch the information. Following are resource IDs which are already implemented.

RES_MEM_ACTIVE
RES_MEM_INACTIVE
RES_MEM_AVAILABLE
RES_MEM_FREE
RES_MEM_TOTAL
RES_MEM_PAGESIZE
RES_MEM_SWAPFREE
RES_MEM_SWAPTOTAL
RES_KERN_COMPILE_TIME
RES_KERN_RELEASE
RES_NET_ALLIFSTAT
RES_NET_IFSTAT
RES_MEM_INFOALL

2: Read single resource info

int res_read(int res_id, void *out, void *hint, int pid, int flags);

This is to read a resource information. A valid resource id should be provided in res_id, out should be properly allocated on the basis of size of resource information, hint should be given where needed. Currently pid and flags are not used, they are for future extensions.

3: Read multiple resource info

If an application wants to read multiple resource information in one call, it can call res_*_blk APIs to do so.

3.1 structs

Following struct holds information about one resource in such case.

typedef struct res_unit {
    int status;
    int res_id;
    void *hint;
    union r_data data;
} res_unit_t;

An array of these form res_blk_t structure as below.

typedef struct res_blk {
    int res_count;
    res_unit_t *res_unit[0];
} res_blk_t;

res_blk_t strcut is used in all res_*_blk interfaces.

3.2 functions

res_blk_t *res_build_blk(int *res_ids, int res_count);

It allocates memory for resources and initiates them properly. res_ids holds an array of valid resource ids and res_count holds number of resource ids. It also initializes struct fields properly.

int res_read_blk(res_blk_t *resblk, int pid, int flags);

Reading bulk resource information. Memory must be properly allocated and all fields should be properly filled to return error free resource information. res_build_blk call is suggested to allocate build res_blk_t structure.

void res_destroy_blk(res_blk_t *resblk);

Free allocated memory from res_build_blk.

Examples

1: Reading total memory

size_t stemp = 0;
res_read(RES_MEM_TOTAL,&stemp,NULL, 0, 0);
printf("MEMTOTAL is: %zu\n", stemp);

2: Reading network interface related statistics for interface named "lo"

res_net_ifstat_t ifstat;
res_read(RES_NET_IFSTAT,&ifstat, (void *)"lo",0, 0);
printf("status for %s: %llu %llu\n", ifstat.ifname,
	ifstat.rx_bytes,
	ifstat.rx_packets
);

3: Reading multiple resource information in one call.

res_blk_t *b = NULL;
int a[NUM] = {RES_MEM_PAGESIZE,
            RES_MEM_TOTAL,
            RES_MEM_AVAILABLE,
            RES_MEM_INFOALL,
            RES_KERN_RELEASE,
            RES_NET_IFSTAT,
            RES_NET_ALLIFSTAT,
            RES_KERN_COMPILE_TIME
            };
b = res_build_blk(a, NUM);
b->res_unit[5]->hint = (void *)"lo";

res_read_blk(b, 0, 0);

printf("pagesize %ld bytes,\n memtotal %ld kb,\n memavailable %ld kb,\n"
        " memfree %ld kb,\n release %s,\n compile time %s\n",
        b->res_unit[0]->data.sz,
        b->res_unit[1]->data.sz,
        b->res_unit[2]->data.sz,
        ((res_mem_infoall_t *)(b->res_unit[3]->data.ptr))->memfree,
        b->res_unit[4]->data.str,
        b->res_unit[7]->data.str
);

res_net_ifstat_t *ip = (res_net_ifstat_t *)b->res_unit[5]->data.ptr;
printf("stat for interface %s: %llu %llu\n", ip->ifname,
    ip->rx_bytes,
    ip->rx_packets
    );

int k = (int)(long long)b->res_unit[6]->hint;
res_net_ifstat_t *ipp = (res_net_ifstat_t *)b->res_unit[6]->data.ptr;
for (int j=0; j< k; j++) {
    printf("stat for interface %s: %llu %llu\n", ipp[j].ifname,
        ipp[j].rx_bytes,
        ipp[j].rx_packets
    );
}

free(ipp);
res_destroy_blk(b);