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Subject[RFC/PATCH 4/5] loop: add execute in place support
[RFC/PATCH 4/5] loop: add execute in place support
The old loop driver in 2.6.11. used the readpage/writepage aops to
transfer data. Now loop can also use read/write and direct_IO on the
file if readpage/writepage are not available. Unlike the old 2.6.11.
version, today's loop driver does work with files that do not have
readpage/writepage. Threrefore, this patch is optional.
This patch adds one more transport method to loop that uses the new
address space operation get_xip_page if available.

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
---
diff -ruN linux-2.6-git/drivers/block/loop.c linux-2.6-git-xip/drivers/block/loop.c
--- linux-2.6-git/drivers/block/loop.c 2005-05-10 14:55:05.000000000 +0200
+++ linux-2.6-git-xip/drivers/block/loop.c 2005-05-10 16:21:49.803071544 +0200
@@ -275,6 +275,83 @@
goto out;
}

+
+static int
+do_lo_send_xip(struct loop_device *lo, struct bio_vec *bvec, int bsize, loff_t pos,
+ struct page* ignored)
+{
+ struct file *file = lo->lo_backing_file; /* kudos to NFsckingS */
+ struct address_space *mapping = file->f_mapping;
+ struct address_space_operations *aops = mapping->a_ops;
+ struct page *page;
+ pgoff_t index;
+ unsigned size, offset, bv_offs;
+ int len;
+ int ret = 0;
+
+ down(&mapping->host->i_sem);
+ index = pos >> PAGE_CACHE_SHIFT;
+ offset = pos & ((pgoff_t)PAGE_CACHE_SIZE - 1);
+ bv_offs = bvec->bv_offset;
+ len = bvec->bv_len;
+ while (len > 0) {
+ sector_t IV;
+ int transfer_result;
+
+ IV = ((sector_t)index << (PAGE_CACHE_SHIFT - 9))+(offset >> 9);
+
+ size = PAGE_CACHE_SIZE - offset;
+ if (size > len)
+ size = len;
+
+ page = aops->get_xip_page(mapping,
+ index*(PAGE_SIZE/512), 0);
+ if (!page)
+ goto fail;
+ if (unlikely(IS_ERR(page))) {
+ if (PTR_ERR(page) == -ENODATA) {
+ /* sparse */
+ page = virt_to_page(empty_zero_page);
+ } else
+ goto fail;
+ } else
+ BUG_ON(!PageUptodate(page));
+
+ transfer_result = lo_do_transfer(lo, WRITE, page, offset,
+ bvec->bv_page, bv_offs,
+ size, IV);
+ if (transfer_result) {
+ char *kaddr;
+
+ /*
+ * The transfer failed, but we still write the data to
+ * keep prepare/commit calls balanced.
+ */
+ printk(KERN_ERR "loop: transfer error block %llu\n",
+ (unsigned long long)index);
+ kaddr = kmap_atomic(page, KM_USER0);
+ memset(kaddr + offset, 0, size);
+ kunmap_atomic(kaddr, KM_USER0);
+ }
+ flush_dcache_page(page);
+ if (transfer_result)
+ goto fail;
+ bv_offs += size;
+ len -= size;
+ offset = 0;
+ index++;
+ pos += size;
+ }
+ up(&mapping->host->i_sem);
+out:
+ return ret;
+
+fail:
+ up(&mapping->host->i_sem);
+ ret = -1;
+ goto out;
+}
+
/**
* __do_lo_send_write - helper for writing data to a loop device
*
@@ -356,8 +433,11 @@
struct page *page = NULL;
int i, ret = 0;

- do_lo_send = do_lo_send_aops;
- if (!(lo->lo_flags & LO_FLAGS_USE_AOPS)) {
+ if (lo->lo_flags & LO_FLAGS_USE_AOPS)
+ do_lo_send = do_lo_send_aops;
+ else if (lo->lo_flags & LO_FLAGS_USE_XIP)
+ do_lo_send = do_lo_send_xip;
+ else {
do_lo_send = do_lo_send_direct_write;
if (lo->transfer != transfer_none) {
page = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
@@ -787,11 +867,13 @@
*/
if (!file->f_op->sendfile)
goto out_putf;
- if (aops->prepare_write && aops->commit_write)
+ if (aops->get_xip_page)
+ lo_flags |= LO_FLAGS_USE_XIP;
+ else if (aops->prepare_write && aops->commit_write)
lo_flags |= LO_FLAGS_USE_AOPS;
- if (!(lo_flags & LO_FLAGS_USE_AOPS) && !file->f_op->write)
+ if (!(lo_flags & (LO_FLAGS_USE_AOPS | LO_FLAGS_USE_XIP))
+ && !file->f_op->write)
lo_flags |= LO_FLAGS_READ_ONLY;
-
lo_blocksize = inode->i_blksize;
error = 0;
} else {
diff -ruN linux-2.6-git/include/linux/loop.h linux-2.6-git-xip/include/linux/loop.h
--- linux-2.6-git/include/linux/loop.h 2005-05-10 14:55:23.000000000 +0200
+++ linux-2.6-git-xip/include/linux/loop.h 2005-05-10 16:21:31.816805872 +0200
@@ -74,6 +74,7 @@
enum {
LO_FLAGS_READ_ONLY = 1,
LO_FLAGS_USE_AOPS = 2,
+ LO_FLAGS_USE_XIP = 4,
};

#include <asm/posix_types.h> /* for __kernel_old_dev_t */

-
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