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eCryptfs: delay writing 0's after llseek until write

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Delay writing 0's out in eCryptfs after a seek past the end of the file
until data is actually written.

http://www.opengroup.org/onlinepubs/009695399/functions/lseek.html

``The lseek() function shall not, by itself, extend the size of a
file.''

Without this fix, applications that lseek() past the end of the file without
writing will experience unexpected behavior.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michael Halcrow
2007-05-23 13:58:15 -07:00
committed by Linus Torvalds
parent 4acb3e2f97
commit 53a2731f93
2 changed files with 38 additions and 63 deletions
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42
fs/ecryptfs/mmap.c
View File

@@ -376,8 +376,15 @@ out:
return 0;
}
static int ecryptfs_prepare_write(struct file *file, struct page *page,
unsigned from, unsigned to)
/**
* eCryptfs does not currently support holes. When writing after a
* seek past the end of the file, eCryptfs fills in 0's through to the
* current location. The code to fill in the 0's to all the
* intermediate pages calls ecryptfs_prepare_write_no_truncate().
*/
static int
ecryptfs_prepare_write_no_truncate(struct file *file, struct page *page,
unsigned from, unsigned to)
{
int rc = 0;
@@ -390,6 +397,31 @@ out:
return rc;
}
static int ecryptfs_prepare_write(struct file *file, struct page *page,
unsigned from, unsigned to)
{
loff_t pos;
int rc = 0;
if (from == 0 && to == PAGE_CACHE_SIZE)
goto out; /* If we are writing a full page, it will be
up to date. */
if (!PageUptodate(page))
rc = ecryptfs_do_readpage(file, page, page->index);
pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
if (pos > i_size_read(page->mapping->host)) {
rc = ecryptfs_truncate(file->f_path.dentry, pos);
if (rc) {
printk(KERN_ERR "Error on attempt to "
"truncate to (higher) offset [%lld];"
" rc = [%d]\n", pos, rc);
goto out;
}
}
out:
return rc;
}
int ecryptfs_writepage_and_release_lower_page(struct page *lower_page,
struct inode *lower_inode,
struct writeback_control *wbc)
@@ -744,10 +776,10 @@ int write_zeros(struct file *file, pgoff_t index, int start, int num_zeros)
rc = PTR_ERR(tmp_page);
goto out;
}
rc = ecryptfs_prepare_write(file, tmp_page, start, start + num_zeros);
if (rc) {
if ((rc = ecryptfs_prepare_write_no_truncate(file, tmp_page, start,
(start + num_zeros)))) {
ecryptfs_printk(KERN_ERR, "Error preparing to write zero's "
"to remainder of page at index [0x%.16x]\n",
"to page at index [0x%.16x]\n",
index);
page_cache_release(tmp_page);
goto out;