mm: write iovec cleanup

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 50 insertions, 50 deletions

diff --git a/mm/filemap.h b/mm/filemap.h
index a1e10a232e92..b500d936cec5 100644
--- a/mm/filemap.h
+++ b/mm/filemap.h
@@ -22,82 +22,82 @@ __filemap_copy_from_user_iovec_inatomic(char *vaddr,
 
 /*
  * 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;
+        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);
+                while (bytes) {
+                        int copy = min(bytes, iov->iov_len - base);
 
-                bytes -= copy;
-                base += copy;
-                if (iov->iov_len == base) {
-                        iov++;
-                        base = 0;
+                        bytes -= copy;
+                        base += copy;
+                        if (iov->iov_len == base) {
+                                iov++;
+                                base = 0;
+                        }
                 }
+                *iovp = iov;
+                *basep = base;
         }
-        *iovp = iov;
-        *basep = base;
 }
 #endif