/*
 *    SE/HMC Drive (Read) Cache Functions
 *
 *    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/mm.h>
#include <linux/jiffies.h>

#include "hmcdrv_ftp.h"
#include "hmcdrv_cache.h"

#define HMCDRV_CACHE_TIMEOUT            30 /* aging timeout in seconds */

/**
 * struct hmcdrv_cache_entry - file cache (only used on read/dir)
 * @id: FTP command ID
 * @content: kernel-space buffer, 4k aligned
 * @len: size of @content cache (0 if caching disabled)
 * @ofs: start of content within file (-1 if no cached content)
 * @fname: file name
 * @fsize: file size
 * @timeout: cache timeout in jiffies
 *
 * Notice that the first three members (id, fname, fsize) are cached on all
 * read/dir requests. But content is cached only under some preconditions.
 * Uncached content is signalled by a negative value of @ofs.
 */
struct hmcdrv_cache_entry {
        enum hmcdrv_ftp_cmdid id;
        char fname[HMCDRV_FTP_FIDENT_MAX];
        size_t fsize;
        loff_t ofs;
        unsigned long timeout;
        void *content;
        size_t len;
};

static int hmcdrv_cache_order; /* cache allocated page order */

static struct hmcdrv_cache_entry hmcdrv_cache_file = {
        .fsize = SIZE_MAX,
        .ofs = -1,
        .len = 0,
        .fname = {'\0'}
};

/**
 * hmcdrv_cache_get() - looks for file data/content in read cache
 * @ftp: pointer to FTP command specification
 *
 * Return: number of bytes read from cache or a negative number if nothing
 * in content cache (for the file/cmd specified in @ftp)
 */
static ssize_t hmcdrv_cache_get(const struct hmcdrv_ftp_cmdspec *ftp)
{
        loff_t pos; /* position in cache (signed) */
        ssize_t len;

        if ((ftp->id != hmcdrv_cache_file.id) ||
            strcmp(hmcdrv_cache_file.fname, ftp->fname))
                return -1;

        if (ftp->ofs >= hmcdrv_cache_file.fsize) /* EOF ? */
                return 0;

        if ((hmcdrv_cache_file.ofs < 0) || /* has content? */
            time_after(jiffies, hmcdrv_cache_file.timeout))
                return -1;

        /* there seems to be cached content - calculate the maximum number
         * of bytes that can be returned (regarding file size and offset)
         */
        len = hmcdrv_cache_file.fsize - ftp->ofs;

        if (len > ftp->len)
                len = ftp->len;

        /* check if the requested chunk falls into our cache (which starts
         * at offset 'hmcdrv_cache_file.ofs' in the file of interest)
         */
        pos = ftp->ofs - hmcdrv_cache_file.ofs;

        if ((pos >= 0) &&
            ((pos + len) <= hmcdrv_cache_file.len)) {

                memcpy(ftp->buf,
                       hmcdrv_cache_file.content + pos,
                       len);
                pr_debug("using cached content of '%s', returning %zd/%zd bytes\n",
                         hmcdrv_cache_file.fname, len,
                         hmcdrv_cache_file.fsize);

                return len;
        }

        return -1;
}

/**
 * hmcdrv_cache_do() - do a HMC drive CD/DVD transfer with cache update
 * @ftp: pointer to FTP command specification
 * @func: FTP transfer function to be used
 *
 * Return: number of bytes read/written or a (negative) error code
 */
static ssize_t hmcdrv_cache_do(const struct hmcdrv_ftp_cmdspec *ftp,
                               hmcdrv_cache_ftpfunc func)
{
        ssize_t len;

        /* only cache content if the read/dir cache really exists
         * (hmcdrv_cache_file.len > 0), is large enough to handle the
         * request (hmcdrv_cache_file.len >= ftp->len) and there is a need
         * to do so (ftp->len > 0)
         */
        if ((ftp->len > 0) && (hmcdrv_cache_file.len >= ftp->len)) {

                /* because the cache is not located at ftp->buf, we have to
                 * assemble a new HMC drive FTP cmd specification (pointing
                 * to our cache, and using the increased size)
                 */
                struct hmcdrv_ftp_cmdspec cftp = *ftp; /* make a copy */
                cftp.buf = hmcdrv_cache_file.content;  /* and update */
                cftp.len = hmcdrv_cache_file.len;      /* buffer data */

                len = func(&cftp, &hmcdrv_cache_file.fsize); /* now do */

                if (len > 0) {
                        pr_debug("caching %zd bytes content for '%s'\n",
                                 len, ftp->fname);

                        if (len > ftp->len)
                                len = ftp->len;

                        hmcdrv_cache_file.ofs = ftp->ofs;
                        hmcdrv_cache_file.timeout = jiffies +
                                HMCDRV_CACHE_TIMEOUT * HZ;
                        memcpy(ftp->buf, hmcdrv_cache_file.content, len);
                }
        } else {
                len = func(ftp, &hmcdrv_cache_file.fsize);
                hmcdrv_cache_file.ofs = -1; /* invalidate content */
        }

        if (len > 0) {
                /* cache some file info (FTP command, file name and file
                 * size) unconditionally
                 */
                strlcpy(hmcdrv_cache_file.fname, ftp->fname,
                        HMCDRV_FTP_FIDENT_MAX);
                hmcdrv_cache_file.id = ftp->id;
                pr_debug("caching cmd %d, file size %zu for '%s'\n",
                         ftp->id, hmcdrv_cache_file.fsize, ftp->fname);
        }

        return len;
}

/**
 * hmcdrv_cache_cmd() - perform a cached HMC drive CD/DVD transfer
 * @ftp: pointer to FTP command specification
 * @func: FTP transfer function to be used
 *
 * Attention: Notice that this function is not reentrant - so the caller
 * must ensure exclusive execution.
 *
 * Return: number of bytes read/written or a (negative) error code
 */
ssize_t hmcdrv_cache_cmd(const struct hmcdrv_ftp_cmdspec *ftp,
                         hmcdrv_cache_ftpfunc func)
{
        ssize_t len;

        if ((ftp->id == HMCDRV_FTP_DIR) || /* read cache */
            (ftp->id == HMCDRV_FTP_NLIST) ||
            (ftp->id == HMCDRV_FTP_GET)) {

                len = hmcdrv_cache_get(ftp);

                if (len >= 0) /* got it from cache ? */
                        return len; /* yes */

                len = hmcdrv_cache_do(ftp, func);

                if (len >= 0)
                        return len;

        } else {
                len = func(ftp, NULL); /* simply do original command */
        }

        /* invalidate the (read) cache in case there was a write operation
         * or an error on read/dir
         */
        hmcdrv_cache_file.id = HMCDRV_FTP_NOOP;
        hmcdrv_cache_file.fsize = LLONG_MAX;
        hmcdrv_cache_file.ofs = -1;

        return len;
}

/**
 * hmcdrv_cache_startup() - startup of HMC drive cache
 * @cachesize: cache size
 *
 * Return: 0 on success, else a (negative) error code
 */
int hmcdrv_cache_startup(size_t cachesize)
{
        if (cachesize > 0) { /* perform caching ? */
                hmcdrv_cache_order = get_order(cachesize);
                hmcdrv_cache_file.content =
                        (void *) __get_free_pages(GFP_KERNEL | GFP_DMA,
                                                  hmcdrv_cache_order);

                if (!hmcdrv_cache_file.content) {
                        pr_err("Allocating the requested cache size of %zu bytes failed\n",
                               cachesize);
                        return -ENOMEM;
                }

                pr_debug("content cache enabled, size is %zu bytes\n",
                         cachesize);
        }

        hmcdrv_cache_file.len = cachesize;
        return 0;
}

/**
 * hmcdrv_cache_shutdown() - shutdown of HMC drive cache
 */
void hmcdrv_cache_shutdown(void)
{
        if (hmcdrv_cache_file.content) {
                free_pages((unsigned long) hmcdrv_cache_file.content,
                           hmcdrv_cache_order);
                hmcdrv_cache_file.content = NULL;
        }

        hmcdrv_cache_file.id = HMCDRV_FTP_NOOP;
        hmcdrv_cache_file.fsize = LLONG_MAX;
        hmcdrv_cache_file.ofs = -1;
        hmcdrv_cache_file.len = 0; /* no cache */
}