[PATCH] generic_file_buffered_write(): handle zero-length iovec segments

[pandora-kernel.git] / mm / filemap.c

diff --git a/mm/filemap.c b/mm/filemap.c
index 807a463..648f2c0 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -828,6 +828,32 @@ grab_cache_page_nowait(struct address_space *mapping, unsigned long index)
 }
 EXPORT_SYMBOL(grab_cache_page_nowait);
 
+/*
+ * CD/DVDs are error prone. When a medium error occurs, the driver may fail
+ * a _large_ part of the i/o request. Imagine the worst scenario:
+ *
+ *      ---R__________________________________________B__________
+ *         ^ reading here                             ^ bad block(assume 4k)
+ *
+ * read(R) => miss => readahead(R...B) => media error => frustrating retries
+ * => failing the whole request => read(R) => read(R+1) =>
+ * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
+ * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
+ * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
+ *
+ * It is going insane. Fix it by quickly scaling down the readahead size.
+ */
+static void shrink_readahead_size_eio(struct file *filp,
+                                       struct file_ra_state *ra)
+{
+       if (!ra->ra_pages)
+               return;
+
+       ra->ra_pages /= 4;
+       printk(KERN_WARNING "Reducing readahead size to %luK\n",
+                       ra->ra_pages << (PAGE_CACHE_SHIFT - 10));
+}
+
 /**
  * do_generic_mapping_read - generic file read routine
  * @mapping:   address_space to be read
@@ -985,6 +1011,7 @@ readpage:
                                }
                                unlock_page(page);
                                error = -EIO;
+                               shrink_readahead_size_eio(filp, &ra);
                                goto readpage_error;
                        }
                        unlock_page(page);
@@ -1522,6 +1549,7 @@ page_not_uptodate:
         * Things didn't work out. Return zero to tell the
         * mm layer so, possibly freeing the page cache page first.
         */
+       shrink_readahead_size_eio(file, ra);
        page_cache_release(page);
        return NULL;
 }
@@ -1892,7 +1920,7 @@ int remove_suid(struct dentry *dentry)
 EXPORT_SYMBOL(remove_suid);
 
 size_t
-__filemap_copy_from_user_iovec(char *vaddr, 
+__filemap_copy_from_user_iovec_inatomic(char *vaddr,
                        const struct iovec *iov, size_t base, size_t bytes)
 {
        size_t copied = 0, left = 0;
@@ -1908,12 +1936,8 @@ __filemap_copy_from_user_iovec(char *vaddr,
                vaddr += copy;
                iov++;
 
-               if (unlikely(left)) {
-                       /* zero the rest of the target like __copy_from_user */
-                       if (bytes)
-                               memset(vaddr, 0, bytes);
+               if (unlikely(left))
                        break;
-               }
        }
        return copied - left;
 }
@@ -2045,7 +2069,7 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
 {
        struct file *file = iocb->ki_filp;
        struct address_space * mapping = file->f_mapping;
-       struct address_space_operations *a_ops = mapping->a_ops;
+       const struct address_space_operations *a_ops = mapping->a_ops;
        struct inode    *inode = mapping->host;
        long            status = 0;
        struct page     *page;
@@ -2071,14 +2095,21 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
        do {
                unsigned long index;
                unsigned long offset;
-               unsigned long maxlen;
                size_t copied;
 
                offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
                index = pos >> PAGE_CACHE_SHIFT;
                bytes = PAGE_CACHE_SIZE - offset;
-               if (bytes > count)
-                       bytes = count;
+
+               /* Limit the size of the copy to the caller's write size */
+               bytes = min(bytes, count);
+
+               /*
+                * Limit the size of the copy to that of the current segment,
+                * because fault_in_pages_readable() doesn't know how to walk
+                * segments.
+                */
+               bytes = min(bytes, cur_iov->iov_len - iov_base);
 
                /*
                 * Bring in the user page that we will copy from _first_.
@@ -2086,10 +2117,7 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
                 * same page as we're writing to, without it being marked
                 * up-to-date.
                 */
-               maxlen = cur_iov->iov_len - iov_base;
-               if (maxlen > bytes)
-                       maxlen = bytes;
-               fault_in_pages_readable(buf, maxlen);
+               fault_in_pages_readable(buf, bytes);
 
                page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
                if (!page) {
@@ -2097,6 +2125,12 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
                        break;
                }
 
+               if (unlikely(bytes == 0)) {
+                       status = 0;
+                       copied = 0;
+                       goto zero_length_segment;
+               }
+
                status = a_ops->prepare_write(file, page, offset, offset+bytes);
                if (unlikely(status)) {
                        loff_t isize = i_size_read(inode);
@@ -2126,7 +2160,8 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
                        page_cache_release(page);
                        continue;
                }
-               if (likely(copied > 0)) {
+zero_length_segment:
+               if (likely(copied >= 0)) {
                        if (!status)
                                status = copied;
 
@@ -2191,7 +2226,7 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
                                unsigned long nr_segs, loff_t *ppos)
 {
        struct file *file = iocb->ki_filp;
-       struct address_space * mapping = file->f_mapping;
+       const struct address_space * mapping = file->f_mapping;
        size_t ocount;          /* original count */
        size_t count;           /* after file limit checks */
        struct inode    *inode = mapping->host;