[PATCH] fat: support ->direct_IO()

This patch add to support of ->direct_IO() for mostly read.

The user of this seems to want to use for streaming read.  So, current direct
I/O has limitation, it can only overwrite.  (For write operation, mainly we
need to handle the hole etc..)

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 73 insertions, 9 deletions

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 932c8d6d1f54..e7f4aa7fc686 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -23,6 +23,7 @@
 #include <linux/mount.h>
 #include <linux/vfs.h>
 #include <linux/parser.h>
+#include <linux/uio.h>
 #include <asm/unaligned.h>
 
 #ifndef CONFIG_FAT_DEFAULT_IOCHARSET
@@ -49,43 +50,77 @@ static int fat_add_cluster(struct inode *inode)
         return err;
 }
 
-static int fat_get_block(struct inode *inode, sector_t iblock,
-                         struct buffer_head *bh_result, int create)
+static int __fat_get_blocks(struct inode *inode, sector_t iblock,
+                            unsigned long *max_blocks,
+                            struct buffer_head *bh_result, int create)
 {
         struct super_block *sb = inode->i_sb;
+        struct msdos_sb_info *sbi = MSDOS_SB(sb);
         sector_t phys;
-        int err;
+        unsigned long mapped_blocks;
+        int err, offset;
 
-        err = fat_bmap(inode, iblock, &phys);
+        err = fat_bmap(inode, iblock, &phys, &mapped_blocks);
         if (err)
                 return err;
         if (phys) {
                 map_bh(bh_result, sb, phys);
+                *max_blocks = min(mapped_blocks, *max_blocks);
                 return 0;
         }
         if (!create)
                 return 0;
+
         if (iblock != MSDOS_I(inode)->mmu_private >> sb->s_blocksize_bits) {
                 fat_fs_panic(sb, "corrupted file size (i_pos %lld, %lld)",
                              MSDOS_I(inode)->i_pos, MSDOS_I(inode)->mmu_private);
                 return -EIO;
         }
-        if (!((unsigned long)iblock & (MSDOS_SB(sb)->sec_per_clus - 1))) {
+
+        offset = (unsigned long)iblock & (sbi->sec_per_clus - 1);
+        if (!offset) {
+                /* TODO: multiple cluster allocation would be desirable. */
                 err = fat_add_cluster(inode);
                 if (err)
                         return err;
         }
-        MSDOS_I(inode)->mmu_private += sb->s_blocksize;
-        err = fat_bmap(inode, iblock, &phys);
+        /* available blocks on this cluster */
+        mapped_blocks = sbi->sec_per_clus - offset;
+
+        *max_blocks = min(mapped_blocks, *max_blocks);
+        MSDOS_I(inode)->mmu_private += *max_blocks << sb->s_blocksize_bits;
+
+        err = fat_bmap(inode, iblock, &phys, &mapped_blocks);
         if (err)
                 return err;
-        if (!phys)
-                BUG();
+        BUG_ON(!phys);
+        BUG_ON(*max_blocks != mapped_blocks);
         set_buffer_new(bh_result);
         map_bh(bh_result, sb, phys);
         return 0;
 }
 
+static int fat_get_blocks(struct inode *inode, sector_t iblock,
+                          unsigned long max_blocks,
+                          struct buffer_head *bh_result, int create)
+{
+        struct super_block *sb = inode->i_sb;
+        int err;
+
+        err = __fat_get_blocks(inode, iblock, &max_blocks, bh_result, create);
+        if (err)
+                return err;
+        bh_result->b_size = max_blocks << sb->s_blocksize_bits;
+        return 0;
+}
+
+static int fat_get_block(struct inode *inode, sector_t iblock,
+                         struct buffer_head *bh_result, int create)
+{
+        unsigned long max_blocks = 1;
+        return __fat_get_blocks(inode, iblock, &max_blocks, bh_result, create);
+}
+
 static int fat_writepage(struct page *page, struct writeback_control *wbc)
 {
         return block_write_full_page(page, fat_get_block, wbc);
@@ -128,6 +163,34 @@ static int fat_commit_write(struct file *file, struct page *page,
         return err;
 }
 
+static ssize_t fat_direct_IO(int rw, struct kiocb *iocb,
+                             const struct iovec *iov,
+                             loff_t offset, unsigned long nr_segs)
+{
+        struct file *file = iocb->ki_filp;
+        struct inode *inode = file->f_mapping->host;
+
+        if (rw == WRITE) {
+                /*
+                 * FIXME: blockdev_direct_IO() doesn't use ->prepare_write(),
+                 * so we need to update the ->mmu_private to block boundary.
+                 *
+                 * But we must fill the remaining area or hole by nul for
+                 * updating ->mmu_private.
+                 */
+                loff_t size = offset + iov_length(iov, nr_segs);
+                if (MSDOS_I(inode)->mmu_private < size)
+                        return -EINVAL;
+        }
+
+        /*
+         * FAT need to use the DIO_LOCKING for avoiding the race
+         * condition of fat_get_block() and ->truncate().
+         */
+        return blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
+                                  offset, nr_segs, fat_get_blocks, NULL);
+}
+
 static sector_t _fat_bmap(struct address_space *mapping, sector_t block)
 {
         return generic_block_bmap(mapping, block, fat_get_block);
@@ -141,6 +204,7 @@ static struct address_space_operations fat_aops = {
         .sync_page      = block_sync_page,
         .prepare_write  = fat_prepare_write,
         .commit_write   = fat_commit_write,
+        .direct_IO      = fat_direct_IO,
         .bmap           = _fat_bmap
 };