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authorDavid Howells <dhowells@redhat.com>2009-11-19 18:11:52 +0000
committerDavid Howells <dhowells@redhat.com>2009-11-19 18:11:52 +0000
commita17754fb8c28af19cd70dcbec6d5b0773b94e0c1 (patch)
treed7c25b217c684153eadbac78ab9b1bbff08b75f6 /fs
parent868411be3f445a83fafbd734f3e426400138add5 (diff)
CacheFiles: Don't write a full page if there's only a partial page to cache
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>
Diffstat (limited to 'fs')
-rw-r--r--fs/cachefiles/interface.c20
-rw-r--r--fs/cachefiles/rdwr.c23
2 files changed, 36 insertions, 7 deletions
diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index dd7f852746c..8e67abf0598 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -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);
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 3304646dae8..5a84fd7109a 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -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);