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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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