/*
 *    HMC Drive FTP Services
 *
 *    Copyright IBM Corp. 2013
 *    Author(s): Ralf Hoppe (rhoppe@de.ibm.com)
 */

#define KMSG_COMPONENT "hmcdrv"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/export.h>

#include <linux/ctype.h>
#include <linux/crc16.h>

#include "hmcdrv_ftp.h"
#include "hmcdrv_cache.h"
#include "sclp_ftp.h"
#include "diag_ftp.h"

/**
 * struct hmcdrv_ftp_ops - HMC drive FTP operations
 * @startup: startup function
 * @shutdown: shutdown function
 * @cmd: FTP transfer function
 */
struct hmcdrv_ftp_ops {
        int (*startup)(void);
        void (*shutdown)(void);
        ssize_t (*transfer)(const struct hmcdrv_ftp_cmdspec *ftp,
                            size_t *fsize);
};

static enum hmcdrv_ftp_cmdid hmcdrv_ftp_cmd_getid(const char *cmd, int len);
static int hmcdrv_ftp_parse(char *cmd, struct hmcdrv_ftp_cmdspec *ftp);

static const struct hmcdrv_ftp_ops *hmcdrv_ftp_funcs; /* current operations */
static DEFINE_MUTEX(hmcdrv_ftp_mutex); /* mutex for hmcdrv_ftp_funcs */
static unsigned hmcdrv_ftp_refcnt; /* start/shutdown reference counter */

/**
 * hmcdrv_ftp_cmd_getid() - determine FTP command ID from a command string
 * @cmd: FTP command string (NOT zero-terminated)
 * @len: length of FTP command string in @cmd
 */
static enum hmcdrv_ftp_cmdid hmcdrv_ftp_cmd_getid(const char *cmd, int len)
{
        /* HMC FTP command descriptor */
        struct hmcdrv_ftp_cmd_desc {
                const char *str;           /* command string */
                enum hmcdrv_ftp_cmdid cmd; /* associated command as enum */
        };

        /* Description of all HMC drive FTP commands
         *
         * Notes:
         * 1. Array size should be a prime number.
         * 2. Do not change the order of commands in table (because the
         *    index is determined by CRC % ARRAY_SIZE).
         * 3. Original command 'nlist' was renamed, else the CRC would
         *    collide with 'append' (see point 2).
         */
        static const struct hmcdrv_ftp_cmd_desc ftpcmds[7] = {

                {.str = "get", /* [0] get (CRC = 0x68eb) */
                 .cmd = HMCDRV_FTP_GET},
                {.str = "dir", /* [1] dir (CRC = 0x6a9e) */
                 .cmd = HMCDRV_FTP_DIR},
                {.str = "delete", /* [2] delete (CRC = 0x53ae) */
                 .cmd = HMCDRV_FTP_DELETE},
                {.str = "nls", /* [3] nls (CRC = 0xf87c) */
                 .cmd = HMCDRV_FTP_NLIST},
                {.str = "put", /* [4] put (CRC = 0xac56) */
                 .cmd = HMCDRV_FTP_PUT},
                {.str = "append", /* [5] append (CRC = 0xf56e) */
                 .cmd = HMCDRV_FTP_APPEND},
                {.str = NULL} /* [6] unused */
        };

        const struct hmcdrv_ftp_cmd_desc *pdesc;

        u16 crc = 0xffffU;

        if (len == 0)
                return HMCDRV_FTP_NOOP; /* error indiactor */

        crc = crc16(crc, cmd, len);
        pdesc = ftpcmds + (crc % ARRAY_SIZE(ftpcmds));
        pr_debug("FTP command '%s' has CRC 0x%04x, at table pos. %lu\n",
                 cmd, crc, (crc % ARRAY_SIZE(ftpcmds)));

        if (!pdesc->str || strncmp(pdesc->str, cmd, len))
                return HMCDRV_FTP_NOOP;

        pr_debug("FTP command '%s' found, with ID %d\n",
                 pdesc->str, pdesc->cmd);

        return pdesc->cmd;
}

/**
 * hmcdrv_ftp_parse() - HMC drive FTP command parser
 * @cmd: FTP command string "<cmd> <filename>"
 * @ftp: Pointer to FTP command specification buffer (output)
 *
 * Return: 0 on success, else a (negative) error code
 */
static int hmcdrv_ftp_parse(char *cmd, struct hmcdrv_ftp_cmdspec *ftp)
{
        char *start;
        int argc = 0;

        ftp->id = HMCDRV_FTP_NOOP;
        ftp->fname = NULL;

        while (*cmd != '\0') {

                while (isspace(*cmd))
                        ++cmd;

                if (*cmd == '\0')
                        break;

                start = cmd;

                switch (argc) {
                case 0: /* 1st argument (FTP command) */
                        while ((*cmd != '\0') && !isspace(*cmd))
                                ++cmd;
                        ftp->id = hmcdrv_ftp_cmd_getid(start, cmd - start);
                        break;
                case 1: /* 2nd / last argument (rest of line) */
                        while ((*cmd != '\0') && !iscntrl(*cmd))
                                ++cmd;
                        ftp->fname = start;
                        /* fall through */
                default:
                        *cmd = '\0';
                        break;
                } /* switch */

                ++argc;
        } /* while */

        if (!ftp->fname || (ftp->id == HMCDRV_FTP_NOOP))
                return -EINVAL;

        return 0;
}

/**
 * hmcdrv_ftp_do() - perform a HMC drive FTP, with data from kernel-space
 * @ftp: pointer to FTP command specification
 *
 * Return: number of bytes read/written or a negative error code
 */
ssize_t hmcdrv_ftp_do(const struct hmcdrv_ftp_cmdspec *ftp)
{
        ssize_t len;

        mutex_lock(&hmcdrv_ftp_mutex);

        if (hmcdrv_ftp_funcs && hmcdrv_ftp_refcnt) {
                pr_debug("starting transfer, cmd %d for '%s' at %lld with %zd bytes\n",
                         ftp->id, ftp->fname, (long long) ftp->ofs, ftp->len);
                len = hmcdrv_cache_cmd(ftp, hmcdrv_ftp_funcs->transfer);
        } else {
                len = -ENXIO;
        }

        mutex_unlock(&hmcdrv_ftp_mutex);
        return len;
}
EXPORT_SYMBOL(hmcdrv_ftp_do);

/**
 * hmcdrv_ftp_probe() - probe for the HMC drive FTP service
 *
 * Return: 0 if service is available, else an (negative) error code
 */
int hmcdrv_ftp_probe(void)
{
        int rc;

        struct hmcdrv_ftp_cmdspec ftp = {
                .id = HMCDRV_FTP_NOOP,
                .ofs = 0,
                .fname = "",
                .len = PAGE_SIZE
        };

        ftp.buf = (void *) get_zeroed_page(GFP_KERNEL | GFP_DMA);

        if (!ftp.buf)
                return -ENOMEM;

        rc = hmcdrv_ftp_startup();

        if (rc)
                goto out;

        rc = hmcdrv_ftp_do(&ftp);
        hmcdrv_ftp_shutdown();

        switch (rc) {
        case -ENOENT: /* no such file/media or currently busy, */
        case -EBUSY:  /* but service seems to be available */
                rc = 0;
                break;
        default: /* leave 'rc' as it is for [0, -EPERM, -E...] */
                if (rc > 0)
                        rc = 0; /* clear length (success) */
                break;
        } /* switch */
out:
        free_page((unsigned long) ftp.buf);
        return rc;
}
EXPORT_SYMBOL(hmcdrv_ftp_probe);

/**
 * hmcdrv_ftp_cmd() - Perform a HMC drive FTP, with data from user-space
 *
 * @cmd: FTP command string "<cmd> <filename>"
 * @offset: file position to read/write
 * @buf: user-space buffer for read/written directory/file
 * @len: size of @buf (read/dir) or number of bytes to write
 *
 * This function must not be called before hmcdrv_ftp_startup() was called.
 *
 * Return: number of bytes read/written or a negative error code
 */
ssize_t hmcdrv_ftp_cmd(char __kernel *cmd, loff_t offset,
                       char __user *buf, size_t len)
{
        int order;

        struct hmcdrv_ftp_cmdspec ftp = {.len = len, .ofs = offset};
        ssize_t retlen = hmcdrv_ftp_parse(cmd, &ftp);

        if (retlen)
                return retlen;

        order = get_order(ftp.len);
        ftp.buf = (void *) __get_free_pages(GFP_KERNEL | GFP_DMA, order);

        if (!ftp.buf)
                return -ENOMEM;

        switch (ftp.id) {
        case HMCDRV_FTP_DIR:
        case HMCDRV_FTP_NLIST:
        case HMCDRV_FTP_GET:
                retlen = hmcdrv_ftp_do(&ftp);

                if ((retlen >= 0) &&
                    copy_to_user(buf, ftp.buf, retlen))
                        retlen = -EFAULT;
                break;

        case HMCDRV_FTP_PUT:
        case HMCDRV_FTP_APPEND:
                if (!copy_from_user(ftp.buf, buf, ftp.len))
                        retlen = hmcdrv_ftp_do(&ftp);
                else
                        retlen = -EFAULT;
                break;

        case HMCDRV_FTP_DELETE:
                retlen = hmcdrv_ftp_do(&ftp);
                break;

        default:
                retlen = -EOPNOTSUPP;
                break;
        }

        free_pages((unsigned long) ftp.buf, order);
        return retlen;
}

/**
 * hmcdrv_ftp_startup() - startup of HMC drive FTP functionality for a
 * dedicated (owner) instance
 *
 * Return: 0 on success, else an (negative) error code
 */
int hmcdrv_ftp_startup(void)
{
        static const struct hmcdrv_ftp_ops hmcdrv_ftp_zvm = {
                .startup = diag_ftp_startup,
                .shutdown = diag_ftp_shutdown,
                .transfer = diag_ftp_cmd
        };

        static const struct hmcdrv_ftp_ops hmcdrv_ftp_lpar = {
                .startup = sclp_ftp_startup,
                .shutdown = sclp_ftp_shutdown,
                .transfer = sclp_ftp_cmd
        };

        int rc = 0;

        mutex_lock(&hmcdrv_ftp_mutex); /* block transfers while start-up */

        if (hmcdrv_ftp_refcnt == 0) {
                if (MACHINE_IS_VM)
                        hmcdrv_ftp_funcs = &hmcdrv_ftp_zvm;
                else if (MACHINE_IS_LPAR || MACHINE_IS_KVM)
                        hmcdrv_ftp_funcs = &hmcdrv_ftp_lpar;
                else
                        rc = -EOPNOTSUPP;

                if (hmcdrv_ftp_funcs)
                        rc = hmcdrv_ftp_funcs->startup();
        }

        if (!rc)
                ++hmcdrv_ftp_refcnt;

        mutex_unlock(&hmcdrv_ftp_mutex);
        return rc;
}
EXPORT_SYMBOL(hmcdrv_ftp_startup);

/**
 * hmcdrv_ftp_shutdown() - shutdown of HMC drive FTP functionality for a
 * dedicated (owner) instance
 */
void hmcdrv_ftp_shutdown(void)
{
        mutex_lock(&hmcdrv_ftp_mutex);
        --hmcdrv_ftp_refcnt;

        if ((hmcdrv_ftp_refcnt == 0) && hmcdrv_ftp_funcs)
                hmcdrv_ftp_funcs->shutdown();

        mutex_unlock(&hmcdrv_ftp_mutex);
}
EXPORT_SYMBOL(hmcdrv_ftp_shutdown);