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    Subject[patch 8/9] mm: generic_file_buffered_write iovec cleanup
    Date
    Hide some of the open-coded nr_segs tests into the iovec helpers. This is
    all to simplify generic_file_buffered_write, because that gets more complex
    in the next patch.

    Signed-off-by: Nick Piggin <npiggin@suse.de>

    Index: linux-2.6/mm/filemap.h
    ===================================================================
    --- linux-2.6.orig/mm/filemap.h
    +++ linux-2.6/mm/filemap.h
    @@ -22,82 +22,82 @@ __filemap_copy_from_user_iovec_inatomic(

    /*
    * Copy as much as we can into the page and return the number of bytes which
    - * were sucessfully copied. If a fault is encountered then clear the page
    - * out to (offset+bytes) and return the number of bytes which were copied.
    - *
    - * NOTE: For this to work reliably we really want copy_from_user_inatomic_nocache
    - * to *NOT* zero any tail of the buffer that it failed to copy. If it does,
    - * and if the following non-atomic copy succeeds, then there is a small window
    - * where the target page contains neither the data before the write, nor the
    - * data after the write (it contains zero). A read at this time will see
    - * data that is inconsistent with any ordering of the read and the write.
    - * (This has been detected in practice).
    + * were sucessfully copied. If a fault is encountered then return the number of
    + * bytes which were copied.
    */
    static inline size_t
    -filemap_copy_from_user(struct page *page, unsigned long offset,
    - const char __user *buf, unsigned bytes)
    +filemap_copy_from_user_atomic(struct page *page, unsigned long offset,
    + const struct iovec *iov, unsigned long nr_segs,
    + size_t base, size_t bytes)
    {
    char *kaddr;
    - int left;
    + size_t copied;

    kaddr = kmap_atomic(page, KM_USER0);
    - left = __copy_from_user_inatomic_nocache(kaddr + offset, buf, bytes);
    + if (likely(nr_segs == 1)) {
    + int left;
    + char __user *buf = iov->iov_base + base;
    + left = __copy_from_user_inatomic_nocache(kaddr + offset,
    + buf, bytes);
    + copied = bytes - left;
    + } else {
    + copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset,
    + iov, base, bytes);
    + }
    kunmap_atomic(kaddr, KM_USER0);

    - if (left != 0) {
    - /* Do it the slow way */
    - kaddr = kmap(page);
    - left = __copy_from_user_nocache(kaddr + offset, buf, bytes);
    - kunmap(page);
    - }
    - return bytes - left;
    + return copied;
    }

    /*
    - * This has the same sideeffects and return value as filemap_copy_from_user().
    - * The difference is that on a fault we need to memset the remainder of the
    - * page (out to offset+bytes), to emulate filemap_copy_from_user()'s
    - * single-segment behaviour.
    + * This has the same sideeffects and return value as
    + * filemap_copy_from_user_atomic().
    + * The difference is that it attempts to resolve faults.
    */
    static inline size_t
    -filemap_copy_from_user_iovec(struct page *page, unsigned long offset,
    - const struct iovec *iov, size_t base, size_t bytes)
    +filemap_copy_from_user(struct page *page, unsigned long offset,
    + const struct iovec *iov, unsigned long nr_segs,
    + size_t base, size_t bytes)
    {
    char *kaddr;
    size_t copied;

    - kaddr = kmap_atomic(page, KM_USER0);
    - copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
    - base, bytes);
    - kunmap_atomic(kaddr, KM_USER0);
    - if (copied != bytes) {
    - kaddr = kmap(page);
    - copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
    - base, bytes);
    - if (bytes - copied)
    - memset(kaddr + offset + copied, 0, bytes - copied);
    - kunmap(page);
    + kaddr = kmap(page);
    + if (likely(nr_segs == 1)) {
    + int left;
    + char __user *buf = iov->iov_base + base;
    + left = __copy_from_user_nocache(kaddr + offset, buf, bytes);
    + copied = bytes - left;
    + } else {
    + copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset,
    + iov, base, bytes);
    }
    + kunmap(page);
    return copied;
    }

    static inline void
    -filemap_set_next_iovec(const struct iovec **iovp, size_t *basep, size_t bytes)
    +filemap_set_next_iovec(const struct iovec **iovp, unsigned long nr_segs,
    + size_t *basep, size_t bytes)
    {
    - const struct iovec *iov = *iovp;
    - size_t base = *basep;
    -
    - while (bytes) {
    - int copy = min(bytes, iov->iov_len - base);
    -
    - bytes -= copy;
    - base += copy;
    - if (iov->iov_len == base) {
    - iov++;
    - base = 0;
    + if (likely(nr_segs == 1)) {
    + *basep += bytes;
    + } else {
    + const struct iovec *iov = *iovp;
    + size_t base = *basep;
    +
    + while (bytes) {
    + int copy = min(bytes, iov->iov_len - base);
    +
    + bytes -= copy;
    + base += copy;
    + if (iov->iov_len == base) {
    + iov++;
    + base = 0;
    + }
    }
    + *iovp = iov;
    + *basep = base;
    }
    - *iovp = iov;
    - *basep = base;
    }
    #endif
    Index: linux-2.6/mm/filemap.c
    ===================================================================
    --- linux-2.6.orig/mm/filemap.c
    +++ linux-2.6/mm/filemap.c
    @@ -1840,12 +1840,7 @@ generic_file_buffered_write(struct kiocb
    /*
    * handle partial DIO write. Adjust cur_iov if needed.
    */
    - if (likely(nr_segs == 1))
    - buf = iov->iov_base + written;
    - else {
    - filemap_set_next_iovec(&cur_iov, &iov_offset, written);
    - buf = cur_iov->iov_base + iov_offset;
    - }
    + filemap_set_next_iovec(&cur_iov, nr_segs, &iov_offset, written);

    do {
    struct page *page;
    @@ -1855,6 +1850,7 @@ generic_file_buffered_write(struct kiocb
    size_t bytes; /* Bytes to write to page */
    size_t copied; /* Bytes copied from user */

    + buf = cur_iov->iov_base + iov_offset;
    offset = (pos & (PAGE_CACHE_SIZE - 1));
    index = pos >> PAGE_CACHE_SHIFT;
    bytes = PAGE_CACHE_SIZE - offset;
    @@ -1886,13 +1882,10 @@ generic_file_buffered_write(struct kiocb
    if (unlikely(status))
    goto fs_write_aop_error;

    - if (likely(nr_segs == 1))
    - copied = filemap_copy_from_user(page, offset,
    - buf, bytes);
    - else
    - copied = filemap_copy_from_user_iovec(page, offset,
    - cur_iov, iov_offset, bytes);
    + copied = filemap_copy_from_user(page, offset,
    + cur_iov, nr_segs, iov_offset, bytes);
    flush_dcache_page(page);
    +
    status = a_ops->commit_write(file, page, offset, offset+bytes);
    if (unlikely(status < 0))
    goto fs_write_aop_error;
    @@ -1903,20 +1896,11 @@ generic_file_buffered_write(struct kiocb
    if (unlikely(status > 0)) /* filesystem did partial write */
    copied = status;

    - if (likely(copied > 0)) {
    - written += copied;
    - count -= copied;
    - pos += copied;
    - buf += copied;
    - if (unlikely(nr_segs > 1)) {
    - filemap_set_next_iovec(&cur_iov,
    - &iov_offset, copied);
    - if (count)
    - buf = cur_iov->iov_base + iov_offset;
    - } else {
    - iov_offset += copied;
    - }
    - }
    + written += copied;
    + count -= copied;
    + pos += copied;
    + filemap_set_next_iovec(&cur_iov, nr_segs, &iov_offset, copied);
    +
    unlock_page(page);
    mark_page_accessed(page);
    page_cache_release(page);
    -
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