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mm: write iovec cleanup
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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 <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Nick Piggin authored and Linus Torvalds committed Oct 16, 2007
1 parent eb2be18 commit 4a9e5ef
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Showing 3 changed files with 67 additions and 86 deletions.
36 changes: 10 additions & 26 deletions mm/filemap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1823,12 +1823,7 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
/*
* 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;
Expand All @@ -1838,6 +1833,7 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
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;
Expand Down Expand Up @@ -1869,13 +1865,10 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
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 || status == AOP_TRUNCATED_PAGE))
goto fs_write_aop_error;
Expand All @@ -1886,20 +1879,11 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
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);
Expand Down
100 changes: 50 additions & 50 deletions mm/filemap.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
17 changes: 7 additions & 10 deletions mm/filemap_xip.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,6 @@
#include <linux/rmap.h>
#include <linux/sched.h>
#include <asm/tlbflush.h>
#include "filemap.h"

/*
* We do use our own empty page to avoid interference with other users
Expand Down Expand Up @@ -288,21 +287,14 @@ __xip_file_write(struct file *filp, const char __user *buf,
unsigned long index;
unsigned long offset;
size_t copied;
char *kaddr;

offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
index = pos >> PAGE_CACHE_SHIFT;
bytes = PAGE_CACHE_SIZE - offset;
if (bytes > count)
bytes = count;

/*
* Bring in the user page that we will copy from _first_.
* Otherwise there's a nasty deadlock on copying from the
* same page as we're writing to, without it being marked
* up-to-date.
*/
fault_in_pages_readable(buf, bytes);

page = a_ops->get_xip_page(mapping,
index*(PAGE_SIZE/512), 0);
if (IS_ERR(page) && (PTR_ERR(page) == -ENODATA)) {
Expand All @@ -319,8 +311,13 @@ __xip_file_write(struct file *filp, const char __user *buf,
break;
}

copied = filemap_copy_from_user(page, offset, buf, bytes);
fault_in_pages_readable(buf, bytes);
kaddr = kmap_atomic(page, KM_USER0);
copied = bytes -
__copy_from_user_inatomic_nocache(kaddr, buf, bytes);
kunmap_atomic(kaddr, KM_USER0);
flush_dcache_page(page);

if (likely(copied > 0)) {
status = copied;

Expand Down

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