// SPDX-License-Identifier: GPL-2.0
#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/vfs.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/mount.h>

#include "fs.h"
#include "../io.h"
#include "debug-internal.h"

#define _STR(x) #x
#define STR(x) _STR(x)

#ifndef SYSFS_MAGIC
#define SYSFS_MAGIC            0x62656572
#endif

#ifndef PROC_SUPER_MAGIC
#define PROC_SUPER_MAGIC       0x9fa0
#endif

#ifndef DEBUGFS_MAGIC
#define DEBUGFS_MAGIC          0x64626720
#endif

#ifndef TRACEFS_MAGIC
#define TRACEFS_MAGIC          0x74726163
#endif

#ifndef HUGETLBFS_MAGIC
#define HUGETLBFS_MAGIC        0x958458f6
#endif

#ifndef BPF_FS_MAGIC
#define BPF_FS_MAGIC           0xcafe4a11
#endif

static const char * const sysfs__known_mountpoints[] = {
        "/sys",
        0,
};

static const char * const procfs__known_mountpoints[] = {
        "/proc",
        0,
};

#ifndef DEBUGFS_DEFAULT_PATH
#define DEBUGFS_DEFAULT_PATH "/sys/kernel/debug"
#endif

static const char * const debugfs__known_mountpoints[] = {
        DEBUGFS_DEFAULT_PATH,
        "/debug",
        0,
};


#ifndef TRACEFS_DEFAULT_PATH
#define TRACEFS_DEFAULT_PATH "/sys/kernel/tracing"
#endif

static const char * const tracefs__known_mountpoints[] = {
        TRACEFS_DEFAULT_PATH,
        "/sys/kernel/debug/tracing",
        "/tracing",
        "/trace",
        0,
};

static const char * const hugetlbfs__known_mountpoints[] = {
        0,
};

static const char * const bpf_fs__known_mountpoints[] = {
        "/sys/fs/bpf",
        0,
};

struct fs {
        const char *             const name;
        const char * const *     const mounts;
        char                    *path;
        pthread_mutex_t          mount_mutex;
        const long               magic;
};

#ifndef TRACEFS_MAGIC
#define TRACEFS_MAGIC 0x74726163
#endif

static void fs__init_once(struct fs *fs);
static const char *fs__mountpoint(const struct fs *fs);
static const char *fs__mount(struct fs *fs);

#define FS(lower_name, fs_name, upper_name)             \
static struct fs fs__##lower_name = {                   \
        .name = #fs_name,                               \
        .mounts = lower_name##__known_mountpoints,      \
        .magic = upper_name##_MAGIC,                    \
        .mount_mutex = PTHREAD_MUTEX_INITIALIZER,       \
};                                                      \
                                                        \
static void lower_name##_init_once(void)                \
{                                                       \
        struct fs *fs = &fs__##lower_name;              \
                                                        \
        fs__init_once(fs);                              \
}                                                       \
                                                        \
const char *lower_name##__mountpoint(void)              \
{                                                       \
        static pthread_once_t init_once = PTHREAD_ONCE_INIT;    \
        struct fs *fs = &fs__##lower_name;              \
                                                        \
        pthread_once(&init_once, lower_name##_init_once);       \
        return fs__mountpoint(fs);                      \
}                                                       \
                                                        \
const char *lower_name##__mount(void)                   \
{                                                       \
        const char *mountpoint = lower_name##__mountpoint();    \
        struct fs *fs = &fs__##lower_name;              \
                                                        \
        if (mountpoint)                                 \
                return mountpoint;                      \
                                                        \
        return fs__mount(fs);                           \
}                                                       \
                                                        \
bool lower_name##__configured(void)                     \
{                                                       \
        return lower_name##__mountpoint() != NULL;      \
}

FS(sysfs, sysfs, SYSFS);
FS(procfs, procfs, PROC_SUPER);
FS(debugfs, debugfs, DEBUGFS);
FS(tracefs, tracefs, TRACEFS);
FS(hugetlbfs, hugetlbfs, HUGETLBFS);
FS(bpf_fs, bpf, BPF_FS);

static bool fs__read_mounts(struct fs *fs)
{
        char type[100];
        FILE *fp;
        char path[PATH_MAX + 1];

        fp = fopen("/proc/mounts", "r");
        if (fp == NULL)
                return false;

        while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
                      path, type) == 2) {

                if (strcmp(type, fs->name) == 0) {
                        fs->path = strdup(path);
                        fclose(fp);
                        return fs->path != NULL;
                }
        }
        fclose(fp);
        return false;
}

static int fs__valid_mount(const char *fs, long magic)
{
        struct statfs st_fs;

        if (statfs(fs, &st_fs) < 0)
                return -ENOENT;
        else if ((long)st_fs.f_type != magic)
                return -ENOENT;

        return 0;
}

static bool fs__check_mounts(struct fs *fs)
{
        const char * const *ptr;

        ptr = fs->mounts;
        while (*ptr) {
                if (fs__valid_mount(*ptr, fs->magic) == 0) {
                        fs->path = strdup(*ptr);
                        if (!fs->path)
                                return false;
                        return true;
                }
                ptr++;
        }

        return false;
}

static void mem_toupper(char *f, size_t len)
{
        while (len) {
                *f = toupper(*f);
                f++;
                len--;
        }
}

/*
 * Check for "NAME_PATH" environment variable to override fs location (for
 * testing). This matches the recommendation in Documentation/admin-guide/sysfs-rules.rst
 * for SYSFS_PATH.
 */
static bool fs__env_override(struct fs *fs)
{
        char *override_path;
        size_t name_len = strlen(fs->name);
        /* name + "_PATH" + '\0' */
        char upper_name[name_len + 5 + 1];

        memcpy(upper_name, fs->name, name_len);
        mem_toupper(upper_name, name_len);
        strcpy(&upper_name[name_len], "_PATH");

        override_path = getenv(upper_name);
        if (!override_path)
                return false;

        fs->path = strdup(override_path);
        if (!fs->path)
                return false;
        return true;
}

static void fs__init_once(struct fs *fs)
{
        if (!fs__env_override(fs) &&
            !fs__check_mounts(fs) &&
            !fs__read_mounts(fs)) {
                assert(!fs->path);
        } else {
                assert(fs->path);
        }
}

static const char *fs__mountpoint(const struct fs *fs)
{
        return fs->path;
}

static const char *mount_overload(struct fs *fs)
{
        size_t name_len = strlen(fs->name);
        /* "PERF_" + name + "_ENVIRONMENT" + '\0' */
        char upper_name[5 + name_len + 12 + 1];

        snprintf(upper_name, name_len, "PERF_%s_ENVIRONMENT", fs->name);
        mem_toupper(upper_name, name_len);

        return getenv(upper_name) ?: *fs->mounts;
}

static const char *fs__mount(struct fs *fs)
{
        const char *mountpoint;

        pthread_mutex_lock(&fs->mount_mutex);

        /* Check if path found inside the mutex to avoid races with other callers of mount. */
        mountpoint = fs__mountpoint(fs);
        if (mountpoint)
                goto out;

        mountpoint = mount_overload(fs);

        if (mount(NULL, mountpoint, fs->name, 0, NULL) == 0 &&
            fs__valid_mount(mountpoint, fs->magic) == 0) {
                fs->path = strdup(mountpoint);
                mountpoint = fs->path;
        }
out:
        pthread_mutex_unlock(&fs->mount_mutex);
        return mountpoint;
}

int filename__read_int(const char *filename, int *value)
{
        char line[64];
        int fd = open(filename, O_RDONLY), err = -1;

        if (fd < 0)
                return -errno;

        if (read(fd, line, sizeof(line)) > 0) {
                *value = atoi(line);
                err = 0;
        }

        close(fd);
        return err;
}

static int filename__read_ull_base(const char *filename,
                                   unsigned long long *value, int base)
{
        char line[64];
        int fd = open(filename, O_RDONLY), err = -1;

        if (fd < 0)
                return -errno;

        if (read(fd, line, sizeof(line)) > 0) {
                *value = strtoull(line, NULL, base);
                if (*value != ULLONG_MAX)
                        err = 0;
        }

        close(fd);
        return err;
}

/*
 * Parses @value out of @filename with strtoull.
 * By using 16 for base to treat the number as hex.
 */
int filename__read_xll(const char *filename, unsigned long long *value)
{
        return filename__read_ull_base(filename, value, 16);
}

/*
 * Parses @value out of @filename with strtoull.
 * By using 0 for base, the strtoull detects the
 * base automatically (see man strtoull).
 */
int filename__read_ull(const char *filename, unsigned long long *value)
{
        return filename__read_ull_base(filename, value, 0);
}

int filename__read_str(const char *filename, char **buf, size_t *sizep)
{
        struct io io;
        char bf[128];
        int err;

        io.fd = open(filename, O_RDONLY);
        if (io.fd < 0)
                return -errno;
        io__init(&io, io.fd, bf, sizeof(bf));
        *buf = NULL;
        err = io__getdelim(&io, buf, sizep, /*delim=*/-1);
        if (err < 0) {
                free(*buf);
                *buf = NULL;
        } else
                err = 0;
        close(io.fd);
        return err;
}

int filename__write_int(const char *filename, int value)
{
        int fd = open(filename, O_WRONLY), err = -1;
        char buf[64];

        if (fd < 0)
                return -errno;

        sprintf(buf, "%d", value);
        if (write(fd, buf, sizeof(buf)) == sizeof(buf))
                err = 0;

        close(fd);
        return err;
}

int procfs__read_str(const char *entry, char **buf, size_t *sizep)
{
        char path[PATH_MAX];
        const char *procfs = procfs__mountpoint();

        if (!procfs)
                return -1;

        snprintf(path, sizeof(path), "%s/%s", procfs, entry);

        return filename__read_str(path, buf, sizep);
}

static int sysfs__read_ull_base(const char *entry,
                                unsigned long long *value, int base)
{
        char path[PATH_MAX];
        const char *sysfs = sysfs__mountpoint();

        if (!sysfs)
                return -1;

        snprintf(path, sizeof(path), "%s/%s", sysfs, entry);

        return filename__read_ull_base(path, value, base);
}

int sysfs__read_xll(const char *entry, unsigned long long *value)
{
        return sysfs__read_ull_base(entry, value, 16);
}

int sysfs__read_ull(const char *entry, unsigned long long *value)
{
        return sysfs__read_ull_base(entry, value, 0);
}

int sysfs__read_int(const char *entry, int *value)
{
        char path[PATH_MAX];
        const char *sysfs = sysfs__mountpoint();

        if (!sysfs)
                return -1;

        snprintf(path, sizeof(path), "%s/%s", sysfs, entry);

        return filename__read_int(path, value);
}

int sysfs__read_str(const char *entry, char **buf, size_t *sizep)
{
        char path[PATH_MAX];
        const char *sysfs = sysfs__mountpoint();

        if (!sysfs)
                return -1;

        snprintf(path, sizeof(path), "%s/%s", sysfs, entry);

        return filename__read_str(path, buf, sizep);
}

int sysfs__read_bool(const char *entry, bool *value)
{
        struct io io;
        char bf[16];
        int ret = 0;
        char path[PATH_MAX];
        const char *sysfs = sysfs__mountpoint();

        if (!sysfs)
                return -1;

        snprintf(path, sizeof(path), "%s/%s", sysfs, entry);
        io.fd = open(path, O_RDONLY);
        if (io.fd < 0)
                return -errno;

        io__init(&io, io.fd, bf, sizeof(bf));
        switch (io__get_char(&io)) {
        case '1':
        case 'y':
        case 'Y':
                *value = true;
                break;
        case '0':
        case 'n':
        case 'N':
                *value = false;
                break;
        default:
                ret = -1;
        }
        close(io.fd);

        return ret;
}
int sysctl__read_int(const char *sysctl, int *value)
{
        char path[PATH_MAX];
        const char *procfs = procfs__mountpoint();

        if (!procfs)
                return -1;

        snprintf(path, sizeof(path), "%s/sys/%s", procfs, sysctl);

        return filename__read_int(path, value);
}

int sysfs__write_int(const char *entry, int value)
{
        char path[PATH_MAX];
        const char *sysfs = sysfs__mountpoint();

        if (!sysfs)
                return -1;

        if (snprintf(path, sizeof(path), "%s/%s", sysfs, entry) >= PATH_MAX)
                return -1;

        return filename__write_int(path, value);
}