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    Subject[PATCH 1/4] fuse: add basic support of iovec[] to fuse_req
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    The patch allows fuse_req to refer to array of iovec-s describing
    layout of user-data over req->pages. fuse_copy_pages() is re-worked to
    support both cased: former layout where pages[] corresponded to <buf, len>
    and newer one where pages[] corresponds to iovec[].

    Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
    ---
    fs/fuse/dev.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++---
    fs/fuse/fuse_i.h | 12 ++++++++++--
    2 files changed, 59 insertions(+), 5 deletions(-)

    diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
    index 7df2b5e..cdae525 100644
    --- a/fs/fuse/dev.c
    +++ b/fs/fuse/dev.c
    @@ -850,9 +850,9 @@ static int fuse_copy_page(struct fuse_copy_state *cs, struct page **pagep,
    return 0;
    }

    -/* Copy pages in the request to/from userspace buffer */
    -static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
    - int zeroing)
    +/* Start from addr(pages[0]) + page_offset. No holes in the middle. */
    +static int fuse_copy_pages_for_buf(struct fuse_copy_state *cs, unsigned nbytes,
    + int zeroing)
    {
    unsigned i;
    struct fuse_req *req = cs->req;
    @@ -874,6 +874,52 @@ static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
    return 0;
    }

    +/* Take iov_offset as offset in iovec[0]. Iterate based on iovec[].iov_len */
    +static int fuse_copy_pages_for_iovec(struct fuse_copy_state *cs,
    + unsigned nbytes, int zeroing)
    +{
    + unsigned i;
    + struct fuse_req *req = cs->req;
    + const struct iovec *iov = req->iovec;
    + unsigned iov_offset = req->iov_offset;
    +
    + for (i = 0; i < req->num_pages && (nbytes || zeroing); i++) {
    + int err;
    + unsigned long user_addr = (unsigned long)iov->iov_base +
    + iov_offset;
    + unsigned offset = user_addr & ~PAGE_MASK;
    + unsigned count = min_t(size_t, PAGE_SIZE - offset,
    + iov->iov_len - iov_offset);
    + count = min(nbytes, count);
    +
    + err = fuse_copy_page(cs, &req->pages[i], offset, count,
    + zeroing);
    + if (err)
    + return err;
    +
    + nbytes -= count;
    +
    + if (count < iov->iov_len - iov_offset) {
    + iov_offset += count;
    + } else {
    + iov++;
    + iov_offset = 0;
    + }
    + }
    +
    + return 0;
    +}
    +
    +/* Copy pages in the request to/from userspace buffer */
    +static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
    + int zeroing)
    +{
    + if (cs->req->iovec)
    + return fuse_copy_pages_for_iovec(cs, nbytes, zeroing);
    + else
    + return fuse_copy_pages_for_buf(cs, nbytes, zeroing);
    +}
    +
    /* Copy a single argument in the request to/from userspace buffer */
    static int fuse_copy_one(struct fuse_copy_state *cs, void *val, unsigned size)
    {
    diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
    index 771fb63..255b7cd 100644
    --- a/fs/fuse/fuse_i.h
    +++ b/fs/fuse/fuse_i.h
    @@ -296,8 +296,16 @@ struct fuse_req {
    /** number of pages in vector */
    unsigned num_pages;

    - /** offset of data on first page */
    - unsigned page_offset;
    + /** If set, it describes layout of user-data in pages[] */
    + const struct iovec *iovec;
    +
    + union {
    + /** offset of data on first page */
    + unsigned page_offset;
    +
    + /** or in first iovec */
    + unsigned iov_offset;
    + };

    /** File used in the request (or NULL) */
    struct fuse_file *ff;


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