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CacheFiles: Don't write a full page if there's only a partial page to cache

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cachefiles_write_page() writes a full page to the backing file for the last
page of the netfs file, even if the netfs file's last page is only a partial
page.

This causes the EOF on the backing file to be extended beyond the EOF of the
netfs, and thus the backing file will be truncated by cachefiles_attr_changed()
called from cachefiles_lookup_object().

So we need to limit the write we make to the backing file on that last page
such that it doesn't push the EOF too far.

Also, if a backing file that has a partial page at the end is expanded, we
discard the partial page and refetch it on the basis that we then have a hole
in the file with invalid data, and should the power go out...  A better way to
deal with this could be to record a note that the partial page contains invalid
data until the correct data is written into it.

This isn't a problem for netfs's that discard the whole backing file if the
file size changes (such as NFS).

Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
David Howells 2009-11-19 18:11:52 +00:00
parent 868411be3f
commit a17754fb8c
3 changed files with 39 additions and 7 deletions
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20
fs/cachefiles/interface.c
View File

@ -404,12 +404,26 @@ static int cachefiles_attr_changed(struct fscache_object *_object)
if (oi_size == ni_size)
return 0;
newattrs.ia_size = ni_size;
newattrs.ia_valid = ATTR_SIZE;
cachefiles_begin_secure(cache, &saved_cred);
mutex_lock(&object->backer->d_inode->i_mutex);
/* if there's an extension to a partial page at the end of the backing
* file, we need to discard the partial page so that we pick up new
* data after it */
if (oi_size & ~PAGE_MASK && ni_size > oi_size) {
_debug("discard tail %llx", oi_size);
newattrs.ia_valid = ATTR_SIZE;
newattrs.ia_size = oi_size & PAGE_MASK;
ret = notify_change(object->backer, &newattrs);
if (ret < 0)
goto truncate_failed;
}
newattrs.ia_valid = ATTR_SIZE;
newattrs.ia_size = ni_size;
ret = notify_change(object->backer, &newattrs);
truncate_failed:
mutex_unlock(&object->backer->d_inode->i_mutex);
cachefiles_end_secure(cache, saved_cred);

23
fs/cachefiles/rdwr.c
View File

@ -803,7 +803,8 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
struct cachefiles_cache *cache;
mm_segment_t old_fs;
struct file *file;
loff_t pos;
loff_t pos, eof;
size_t len;
void *data;
int ret;
@ -837,15 +838,29 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
ret = -EIO;
if (file->f_op->write) {
pos = (loff_t) page->index << PAGE_SHIFT;
/* we mustn't write more data than we have, so we have
* to beware of a partial page at EOF */
eof = object->fscache.store_limit_l;
len = PAGE_SIZE;
if (eof & ~PAGE_MASK) {
ASSERTCMP(pos, <, eof);
if (eof - pos < PAGE_SIZE) {
_debug("cut short %llx to %llx",
pos, eof);
len = eof - pos;
ASSERTCMP(pos + len, ==, eof);
}
}
data = kmap(page);
old_fs = get_fs();
set_fs(KERNEL_DS);
ret = file->f_op->write(
file, (const void __user *) data, PAGE_SIZE,
&pos);
file, (const void __user *) data, len, &pos);
set_fs(old_fs);
kunmap(page);
if (ret != PAGE_SIZE)
if (ret != len)
ret = -EIO;
}
fput(file);

3
include/linux/fscache-cache.h
View File

@ -395,6 +395,7 @@ struct fscache_object {
struct rb_node objlist_link; /* link in global object list */
#endif
pgoff_t store_limit; /* current storage limit */
loff_t store_limit_l; /* current storage limit */
};
extern const char *fscache_object_states[];
@ -439,6 +440,7 @@ void fscache_object_init(struct fscache_object *object,
object->events = object->event_mask = 0;
object->flags = 0;
object->store_limit = 0;
object->store_limit_l = 0;
object->cache = cache;
object->cookie = cookie;
object->parent = NULL;
@ -491,6 +493,7 @@ static inline void fscache_object_lookup_error(struct fscache_object *object)
static inline
void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
{
object->store_limit_l = i_size;
object->store_limit = i_size >> PAGE_SHIFT;
if (i_size & ~PAGE_MASK)
object->store_limit++;