buffer.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2010  Miklos Szeredi <miklos@szeredi.hu>

  Functions for dealing with `struct fuse_buf` and `struct
  fuse_bufvec`.

  This program can be distributed under the terms of the GNU LGPLv2.
  See the file COPYING.LIB
*/

#define _GNU_SOURCE

#include "config.h"
#include "fuse_i.h"
#include "fuse_lowlevel.h"
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <assert.h>

size_t fuse_buf_size(const struct fuse_bufvec *bufv)
{
        size_t i;
        size_t size = 0;

        for (i = 0; i < bufv->count; i++) {
                if (bufv->buf[i].size == SIZE_MAX)
                        size = SIZE_MAX;
                else
                        size += bufv->buf[i].size;
        }

        return size;
}

static size_t min_size(size_t s1, size_t s2)
{
        return s1 < s2 ? s1 : s2;
}

static ssize_t fuse_buf_write(const struct fuse_buf *dst, size_t dst_off,
                              const struct fuse_buf *src, size_t src_off,
                              size_t len)
{
        ssize_t res = 0;
        size_t copied = 0;

        while (len) {
                if (dst->flags & FUSE_BUF_FD_SEEK) {
                        res = pwrite(dst->fd, (char *)src->mem + src_off, len,
                                     dst->pos + dst_off);
                } else {
                        res = write(dst->fd, (char *)src->mem + src_off, len);
                }
                if (res == -1) {
                        if (!copied)
                                return -errno;
                        break;
                }
                if (res == 0)
                        break;

                copied += res;
                if (!(dst->flags & FUSE_BUF_FD_RETRY))
                        break;

                src_off += res;
                dst_off += res;
                len -= res;
        }

        return copied;
}

static ssize_t fuse_buf_read(const struct fuse_buf *dst, size_t dst_off,
                             const struct fuse_buf *src, size_t src_off,
                             size_t len)
{
        ssize_t res = 0;
        size_t copied = 0;

        while (len) {
                if (src->flags & FUSE_BUF_FD_SEEK) {
                        res = pread(src->fd, (char *)dst->mem + dst_off, len,
                                     src->pos + src_off);
                } else {
                        res = read(src->fd, (char *)dst->mem + dst_off, len);
                }
                if (res == -1) {
                        if (!copied)
                                return -errno;
                        break;
                }
                if (res == 0)
                        break;

                copied += res;
                if (!(src->flags & FUSE_BUF_FD_RETRY))
                        break;

                dst_off += res;
                src_off += res;
                len -= res;
        }

        return copied;
}

static ssize_t fuse_buf_fd_to_fd(const struct fuse_buf *dst, size_t dst_off,
                                 const struct fuse_buf *src, size_t src_off,
                                 size_t len)
{
        char buf[4096];
        struct fuse_buf tmp = {
                .size = sizeof(buf),
                .flags = 0,
        };
        ssize_t res;
        size_t copied = 0;

        tmp.mem = buf;

        while (len) {
                size_t this_len = min_size(tmp.size, len);
                size_t read_len;

                res = fuse_buf_read(&tmp, 0, src, src_off, this_len);
                if (res < 0) {
                        if (!copied)
                                return res;
                        break;
                }
                if (res == 0)
                        break;

                read_len = res;
                res = fuse_buf_write(dst, dst_off, &tmp, 0, read_len);
                if (res < 0) {
                        if (!copied)
                                return res;
                        break;
                }
                if (res == 0)
                        break;

                copied += res;

                if (res < this_len)
                        break;

                dst_off += res;
                src_off += res;
                len -= res;
        }

        return copied;
}

#ifdef HAVE_SPLICE
static ssize_t fuse_buf_splice(const struct fuse_buf *dst, size_t dst_off,
                               const struct fuse_buf *src, size_t src_off,
                               size_t len, enum fuse_buf_copy_flags flags)
{
        int splice_flags = 0;
        off_t *srcpos = NULL;
        off_t *dstpos = NULL;
        off_t srcpos_val;
        off_t dstpos_val;
        ssize_t res;
        size_t copied = 0;

        if (flags & FUSE_BUF_SPLICE_MOVE)
                splice_flags |= SPLICE_F_MOVE;
        if (flags & FUSE_BUF_SPLICE_NONBLOCK)
                splice_flags |= SPLICE_F_NONBLOCK;

        if (src->flags & FUSE_BUF_FD_SEEK) {
                srcpos_val = src->pos + src_off;
                srcpos = &srcpos_val;
        }
        if (dst->flags & FUSE_BUF_FD_SEEK) {
                dstpos_val = dst->pos + dst_off;
                dstpos = &dstpos_val;
        }

        while (len) {
                res = splice(src->fd, srcpos, dst->fd, dstpos, len,
                             splice_flags);
                if (res == -1) {
                        if (copied)
                                break;

                        if (errno != EINVAL || (flags & FUSE_BUF_FORCE_SPLICE))
                                return -errno;

                        /* Maybe splice is not supported for this combination */
                        return fuse_buf_fd_to_fd(dst, dst_off, src, src_off,
                                                 len);
                }
                if (res == 0)
                        break;

                copied += res;
                if (!(src->flags & FUSE_BUF_FD_RETRY) &&
                    !(dst->flags & FUSE_BUF_FD_RETRY)) {
                        break;
                }

                len -= res;
        }

        return copied;
}
#else
static ssize_t fuse_buf_splice(const struct fuse_buf *dst, size_t dst_off,
                               const struct fuse_buf *src, size_t src_off,
                               size_t len, enum fuse_buf_copy_flags flags)
{
        (void) flags;

        return fuse_buf_fd_to_fd(dst, dst_off, src, src_off, len);
}
#endif


static ssize_t fuse_buf_copy_one(const struct fuse_buf *dst, size_t dst_off,
                                 const struct fuse_buf *src, size_t src_off,
                                 size_t len, enum fuse_buf_copy_flags flags)
{
        int src_is_fd = src->flags & FUSE_BUF_IS_FD;
        int dst_is_fd = dst->flags & FUSE_BUF_IS_FD;

        if (!src_is_fd && !dst_is_fd) {
                char *dstmem = (char *)dst->mem + dst_off;
                char *srcmem = (char *)src->mem + src_off;

                if (dstmem != srcmem) {
                        if (dstmem + len <= srcmem || srcmem + len <= dstmem)
                                memcpy(dstmem, srcmem, len);
                        else
                                memmove(dstmem, srcmem, len);
                }

                return len;
        } else if (!src_is_fd) {
                return fuse_buf_write(dst, dst_off, src, src_off, len);
        } else if (!dst_is_fd) {
                return fuse_buf_read(dst, dst_off, src, src_off, len);
        } else if (flags & FUSE_BUF_NO_SPLICE) {
                return fuse_buf_fd_to_fd(dst, dst_off, src, src_off, len);
        } else {
                return fuse_buf_splice(dst, dst_off, src, src_off, len, flags);
        }
}

static const struct fuse_buf *fuse_bufvec_current(struct fuse_bufvec *bufv)
{
        if (bufv->idx < bufv->count)
                return &bufv->buf[bufv->idx];
        else
                return NULL;
}

static int fuse_bufvec_advance(struct fuse_bufvec *bufv, size_t len)
{
        const struct fuse_buf *buf = fuse_bufvec_current(bufv);

        bufv->off += len;
        assert(bufv->off <= buf->size);
        if (bufv->off == buf->size) {
                assert(bufv->idx < bufv->count);
                bufv->idx++;
                if (bufv->idx == bufv->count)
                        return 0;
                bufv->off = 0;
        }
        return 1;
}

ssize_t fuse_buf_copy(struct fuse_bufvec *dstv, struct fuse_bufvec *srcv,
                      enum fuse_buf_copy_flags flags)
{
        size_t copied = 0;

        if (dstv == srcv)
                return fuse_buf_size(dstv);

        for (;;) {
                const struct fuse_buf *src = fuse_bufvec_current(srcv);
                const struct fuse_buf *dst = fuse_bufvec_current(dstv);
                size_t src_len;
                size_t dst_len;
                size_t len;
                ssize_t res;

                if (src == NULL || dst == NULL)
                        break;

                src_len = src->size - srcv->off;
                dst_len = dst->size - dstv->off;
                len = min_size(src_len, dst_len);

                res = fuse_buf_copy_one(dst, dstv->off, src, srcv->off, len, flags);
                if (res < 0) {
                        if (!copied)
                                return res;
                        break;
                }
                copied += res;

                if (!fuse_bufvec_advance(srcv, res) ||
                    !fuse_bufvec_advance(dstv, res))
                        break;

                if (res < len)
                        break;
        }

        return copied;
}