// SPDX-License-Identifier: GPL-2.0
/*
 * FUSE inode io modes.
 *
 * Copyright (c) 2024 CTERA Networks.
 */

#include "fuse_i.h"

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/file.h>
#include <linux/fs.h>

/*
 * Return true if need to wait for new opens in caching mode.
 */
static inline bool fuse_is_io_cache_wait(struct fuse_inode *fi)
{
        return READ_ONCE(fi->iocachectr) < 0 && !fuse_inode_backing(fi);
}

/*
 * Called on cached file open() and on first mmap() of direct_io file.
 * Takes cached_io inode mode reference to be dropped on file release.
 *
 * Blocks new parallel dio writes and waits for the in-progress parallel dio
 * writes to complete.
 */
int fuse_file_cached_io_open(struct inode *inode, struct fuse_file *ff)
{
        struct fuse_inode *fi = get_fuse_inode(inode);

        /* There are no io modes if server does not implement open */
        if (!ff->args)
                return 0;

        spin_lock(&fi->lock);
        /*
         * Setting the bit advises new direct-io writes to use an exclusive
         * lock - without it the wait below might be forever.
         */
        while (fuse_is_io_cache_wait(fi)) {
                set_bit(FUSE_I_CACHE_IO_MODE, &fi->state);
                spin_unlock(&fi->lock);
                wait_event(fi->direct_io_waitq, !fuse_is_io_cache_wait(fi));
                spin_lock(&fi->lock);
        }

        /*
         * Check if inode entered passthrough io mode while waiting for parallel
         * dio write completion.
         */
        if (fuse_inode_backing(fi)) {
                clear_bit(FUSE_I_CACHE_IO_MODE, &fi->state);
                spin_unlock(&fi->lock);
                return -ETXTBSY;
        }

        WARN_ON(ff->iomode == IOM_UNCACHED);
        if (ff->iomode == IOM_NONE) {
                ff->iomode = IOM_CACHED;
                if (fi->iocachectr == 0)
                        set_bit(FUSE_I_CACHE_IO_MODE, &fi->state);
                fi->iocachectr++;
        }
        spin_unlock(&fi->lock);
        return 0;
}

static void fuse_file_cached_io_release(struct fuse_file *ff,
                                        struct fuse_inode *fi)
{
        spin_lock(&fi->lock);
        WARN_ON(fi->iocachectr <= 0);
        WARN_ON(ff->iomode != IOM_CACHED);
        ff->iomode = IOM_NONE;
        fi->iocachectr--;
        if (fi->iocachectr == 0)
                clear_bit(FUSE_I_CACHE_IO_MODE, &fi->state);
        spin_unlock(&fi->lock);
}

/* Start strictly uncached io mode where cache access is not allowed */
int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
{
        struct fuse_backing *oldfb;
        int err = 0;

        spin_lock(&fi->lock);
        /* deny conflicting backing files on same fuse inode */
        oldfb = fuse_inode_backing(fi);
        if (fb && oldfb && oldfb != fb) {
                err = -EBUSY;
                goto unlock;
        }
        if (fi->iocachectr > 0) {
                err = -ETXTBSY;
                goto unlock;
        }
        fi->iocachectr--;

        /* fuse inode holds a single refcount of backing file */
        if (fb && !oldfb) {
                oldfb = fuse_inode_backing_set(fi, fb);
                WARN_ON_ONCE(oldfb != NULL);
        } else {
                fuse_backing_put(fb);
        }
unlock:
        spin_unlock(&fi->lock);
        return err;
}

/* Takes uncached_io inode mode reference to be dropped on file release */
static int fuse_file_uncached_io_open(struct inode *inode,
                                      struct fuse_file *ff,
                                      struct fuse_backing *fb)
{
        struct fuse_inode *fi = get_fuse_inode(inode);
        int err;

        err = fuse_inode_uncached_io_start(fi, fb);
        if (err)
                return err;

        WARN_ON(ff->iomode != IOM_NONE);
        ff->iomode = IOM_UNCACHED;
        return 0;
}

void fuse_inode_uncached_io_end(struct fuse_inode *fi)
{
        struct fuse_backing *oldfb = NULL;

        spin_lock(&fi->lock);
        WARN_ON(fi->iocachectr >= 0);
        fi->iocachectr++;
        if (!fi->iocachectr) {
                wake_up(&fi->direct_io_waitq);
                oldfb = fuse_inode_backing_set(fi, NULL);
        }
        spin_unlock(&fi->lock);
        if (oldfb)
                fuse_backing_put(oldfb);
}

/* Drop uncached_io reference from passthrough open */
static void fuse_file_uncached_io_release(struct fuse_file *ff,
                                          struct fuse_inode *fi)
{
        WARN_ON(ff->iomode != IOM_UNCACHED);
        ff->iomode = IOM_NONE;
        fuse_inode_uncached_io_end(fi);
}

/*
 * Open flags that are allowed in combination with FOPEN_PASSTHROUGH.
 * A combination of FOPEN_PASSTHROUGH and FOPEN_DIRECT_IO means that read/write
 * operations go directly to the server, but mmap is done on the backing file.
 * FOPEN_PASSTHROUGH mode should not co-exist with any users of the fuse inode
 * page cache, so FOPEN_KEEP_CACHE is a strange and undesired combination.
 */
#define FOPEN_PASSTHROUGH_MASK \
        (FOPEN_PASSTHROUGH | FOPEN_DIRECT_IO | FOPEN_PARALLEL_DIRECT_WRITES | \
         FOPEN_NOFLUSH)

static int fuse_file_passthrough_open(struct inode *inode, struct file *file)
{
        struct fuse_file *ff = file->private_data;
        struct fuse_conn *fc = get_fuse_conn(inode);
        struct fuse_backing *fb;
        int err;

        /* Check allowed conditions for file open in passthrough mode */
        if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH) || !fc->passthrough ||
            (ff->open_flags & ~FOPEN_PASSTHROUGH_MASK))
                return -EINVAL;

        fb = fuse_passthrough_open(file, ff->args->open_outarg.backing_id);
        if (IS_ERR(fb))
                return PTR_ERR(fb);

        /* First passthrough file open denies caching inode io mode */
        err = fuse_file_uncached_io_open(inode, ff, fb);
        if (!err)
                return 0;

        fuse_passthrough_release(ff, fb);
        fuse_backing_put(fb);

        return err;
}

/* Request access to submit new io to inode via open file */
int fuse_file_io_open(struct file *file, struct inode *inode)
{
        struct fuse_file *ff = file->private_data;
        struct fuse_inode *fi = get_fuse_inode(inode);
        int err;

        /*
         * io modes are not relevant with DAX and with server that does not
         * implement open.
         */
        if (FUSE_IS_DAX(inode) || !ff->args)
                return 0;

        /*
         * Server is expected to use FOPEN_PASSTHROUGH for all opens of an inode
         * which is already open for passthrough.
         */
        err = -EINVAL;
        if (fuse_inode_backing(fi) && !(ff->open_flags & FOPEN_PASSTHROUGH))
                goto fail;

        /*
         * FOPEN_PARALLEL_DIRECT_WRITES requires FOPEN_DIRECT_IO.
         */
        if (!(ff->open_flags & FOPEN_DIRECT_IO))
                ff->open_flags &= ~FOPEN_PARALLEL_DIRECT_WRITES;

        /*
         * First passthrough file open denies caching inode io mode.
         * First caching file open enters caching inode io mode.
         *
         * Note that if user opens a file open with O_DIRECT, but server did
         * not specify FOPEN_DIRECT_IO, a later fcntl() could remove O_DIRECT,
         * so we put the inode in caching mode to prevent parallel dio.
         */
        if ((ff->open_flags & FOPEN_DIRECT_IO) &&
            !(ff->open_flags & FOPEN_PASSTHROUGH))
                return 0;

        if (ff->open_flags & FOPEN_PASSTHROUGH)
                err = fuse_file_passthrough_open(inode, file);
        else
                err = fuse_file_cached_io_open(inode, ff);
        if (err)
                goto fail;

        return 0;

fail:
        pr_debug("failed to open file in requested io mode (open_flags=0x%x, err=%i).\n",
                 ff->open_flags, err);
        /*
         * The file open mode determines the inode io mode.
         * Using incorrect open mode is a server mistake, which results in
         * user visible failure of open() with EIO error.
         */
        return -EIO;
}

/* No more pending io and no new io possible to inode via open/mmapped file */
void fuse_file_io_release(struct fuse_file *ff, struct inode *inode)
{
        struct fuse_inode *fi = get_fuse_inode(inode);

        /*
         * Last passthrough file close allows caching inode io mode.
         * Last caching file close exits caching inode io mode.
         */
        switch (ff->iomode) {
        case IOM_NONE:
                /* Nothing to do */
                break;
        case IOM_UNCACHED:
                fuse_file_uncached_io_release(ff, fi);
                break;
        case IOM_CACHED:
                fuse_file_cached_io_release(ff, fi);
                break;
        }
}