// SPDX-License-Identifier: GPL-2.0
#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 <unistd.h>
#include <sys/mount.h>

#include "fs.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__fs_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              *name;
        const char * const      *mounts;
        char                     path[PATH_MAX];
        bool                     found;
        bool                     checked;
        long                     magic;
};

enum {
        FS__SYSFS   = 0,
        FS__PROCFS  = 1,
        FS__DEBUGFS = 2,
        FS__TRACEFS = 3,
        FS__HUGETLBFS = 4,
        FS__BPF_FS = 5,
};

#ifndef TRACEFS_MAGIC
#define TRACEFS_MAGIC 0x74726163
#endif

static struct fs fs__entries[] = {
        [FS__SYSFS] = {
                .name   = "sysfs",
                .mounts = sysfs__fs_known_mountpoints,
                .magic  = SYSFS_MAGIC,
                .checked = false,
        },
        [FS__PROCFS] = {
                .name   = "proc",
                .mounts = procfs__known_mountpoints,
                .magic  = PROC_SUPER_MAGIC,
                .checked = false,
        },
        [FS__DEBUGFS] = {
                .name   = "debugfs",
                .mounts = debugfs__known_mountpoints,
                .magic  = DEBUGFS_MAGIC,
                .checked = false,
        },
        [FS__TRACEFS] = {
                .name   = "tracefs",
                .mounts = tracefs__known_mountpoints,
                .magic  = TRACEFS_MAGIC,
                .checked = false,
        },
        [FS__HUGETLBFS] = {
                .name   = "hugetlbfs",
                .mounts = hugetlbfs__known_mountpoints,
                .magic  = HUGETLBFS_MAGIC,
                .checked = false,
        },
        [FS__BPF_FS] = {
                .name   = "bpf",
                .mounts = bpf_fs__known_mountpoints,
                .magic  = BPF_FS_MAGIC,
                .checked = false,
        },
};

static bool fs__read_mounts(struct fs *fs)
{
        bool found = false;
        char type[100];
        FILE *fp;

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

        while (!found &&
               fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
                      fs->path, type) == 2) {

                if (strcmp(type, fs->name) == 0)
                        found = true;
        }

        fclose(fp);
        fs->checked = true;
        return fs->found = found;
}

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->found = true;
                        strcpy(fs->path, *ptr);
                        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->found = true;
        fs->checked = true;
        strncpy(fs->path, override_path, sizeof(fs->path) - 1);
        fs->path[sizeof(fs->path) - 1] = '\0';
        return true;
}

static const char *fs__get_mountpoint(struct fs *fs)
{
        if (fs__env_override(fs))
                return fs->path;

        if (fs__check_mounts(fs))
                return fs->path;

        if (fs__read_mounts(fs))
                return fs->path;

        return NULL;
}

static const char *fs__mountpoint(int idx)
{
        struct fs *fs = &fs__entries[idx];

        if (fs->found)
                return (const char *)fs->path;

        /* the mount point was already checked for the mount point
         * but and did not exist, so return NULL to avoid scanning again.
         * This makes the found and not found paths cost equivalent
         * in case of multiple calls.
         */
        if (fs->checked)
                return NULL;

        return fs__get_mountpoint(fs);
}

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(int idx)
{
        struct fs *fs = &fs__entries[idx];
        const char *mountpoint;

        if (fs__mountpoint(idx))
                return (const char *)fs->path;

        mountpoint = mount_overload(fs);

        if (mount(NULL, mountpoint, fs->name, 0, NULL) < 0)
                return NULL;

        return fs__check_mounts(fs) ? fs->path : NULL;
}

#define FS(name, idx)                           \
const char *name##__mountpoint(void)            \
{                                               \
        return fs__mountpoint(idx);             \
}                                               \
                                                \
const char *name##__mount(void)                 \
{                                               \
        return fs__mount(idx);                  \
}                                               \
                                                \
bool name##__configured(void)                   \
{                                               \
        return name##__mountpoint() != NULL;    \
}

FS(sysfs,   FS__SYSFS);
FS(procfs,  FS__PROCFS);
FS(debugfs, FS__DEBUGFS);
FS(tracefs, FS__TRACEFS);
FS(hugetlbfs, FS__HUGETLBFS);
FS(bpf_fs, FS__BPF_FS);

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

        if (fd < 0)
                return -1;

        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 -1;

        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);
}

#define STRERR_BUFSIZE  128     /* For the buffer size of strerror_r */

int filename__read_str(const char *filename, char **buf, size_t *sizep)
{
        size_t size = 0, alloc_size = 0;
        void *bf = NULL, *nbf;
        int fd, n, err = 0;
        char sbuf[STRERR_BUFSIZE];

        fd = open(filename, O_RDONLY);
        if (fd < 0)
                return -errno;

        do {
                if (size == alloc_size) {
                        alloc_size += BUFSIZ;
                        nbf = realloc(bf, alloc_size);
                        if (!nbf) {
                                err = -ENOMEM;
                                break;
                        }

                        bf = nbf;
                }

                n = read(fd, bf + size, alloc_size - size);
                if (n < 0) {
                        if (size) {
                                pr_warn("read failed %d: %s\n", errno,
                                        strerror_r(errno, sbuf, sizeof(sbuf)));
                                err = 0;
                        } else
                                err = -errno;

                        break;
                }

                size += n;
        } while (n > 0);

        if (!err) {
                *sizep = size;
                *buf   = bf;
        } else
                free(bf);

        close(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 err;

        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)
{
        char *buf;
        size_t size;
        int ret;

        ret = sysfs__read_str(entry, &buf, &size);
        if (ret < 0)
                return ret;

        switch (buf[0]) {
        case '1':
        case 'y':
        case 'Y':
                *value = true;
                break;
        case '0':
        case 'n':
        case 'N':
                *value = false;
                break;
        default:
                ret = -1;
        }

        free(buf);

        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);
}