* RE: [syzbot ci] Re: exfat: add limited FALLOC_FL_ZERO_RANGE support
2026-03-20 8:16 ` [syzbot ci] Re: exfat: add limited FALLOC_FL_ZERO_RANGE support syzbot ci
@ 2026-03-22 12:35 ` David Timber
2026-03-22 12:38 ` syzbot ci
0 siblings, 1 reply; 3+ messages in thread
From: David Timber @ 2026-03-22 12:35 UTC (permalink / raw)
To: syzbot ci, linkinjeon, linux-fsdevel, linux-kernel, sj1557.seo,
yuezhang.mo
Cc: syzbot, syzkaller-bugs
#syz test
diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index 2daf0dbabb24..dfa5fc89f77d 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -36,7 +36,8 @@ static int exfat_cont_expand(struct inode *inode, loff_t size)
num_clusters = EXFAT_B_TO_CLU(exfat_ondisk_size(inode), sbi);
new_num_clusters = EXFAT_B_TO_CLU_ROUND_UP(size, sbi);
- if (new_num_clusters == num_clusters)
+ WARN_ON(new_num_clusters < num_clusters);
+ if (new_num_clusters <= num_clusters)
goto out;
if (num_clusters) {
@@ -94,35 +95,87 @@ static int exfat_cont_expand(struct inode *inode, loff_t size)
/*
* Preallocate space for a file. This implements exfat's fallocate file
* operation, which gets called from sys_fallocate system call. User space
- * requests len bytes at offset. In contrary to fat, we only support
- * FALLOC_FL_ALLOCATE_RANGE because by leaving the valid data length(VDL)
- * field, it is unnecessary to zero out the newly allocated clusters.
+ * requests len bytes at offset.
+ *
+ * In contrary to fat, FALLOC_FL_ALLOCATE_RANGE can be done without zeroing out
+ * the newly allocated clusters by leaving the valid data length(VDL) field
+ * unchanged.
+ *
+ * Due to the inherent limitation of the VDL scheme, FALLOC_FL_ZERO_RANGE is
+ * only possible when the requested range covers EOF.
*/
static long exfat_fallocate(struct file *file, int mode,
loff_t offset, loff_t len)
{
struct inode *inode = file->f_mapping->host;
- loff_t newsize = offset + len;
+ loff_t newsize, isize;
int err = 0;
/* No support for other modes */
- if (mode != FALLOC_FL_ALLOCATE_RANGE)
+ switch (mode) {
+ case FALLOC_FL_ALLOCATE_RANGE:
+ case FALLOC_FL_ZERO_RANGE:
+ case FALLOC_FL_ZERO_RANGE|FALLOC_FL_KEEP_SIZE:
+ break;
+ default:
return -EOPNOTSUPP;
+ }
/* No support for dir */
if (!S_ISREG(inode->i_mode))
- return -EOPNOTSUPP;
+ return mode & FALLOC_FL_ZERO_RANGE ? -EINVAL : -EOPNOTSUPP;
if (unlikely(exfat_forced_shutdown(inode->i_sb)))
return -EIO;
inode_lock(inode);
- if (newsize <= i_size_read(inode))
- goto error;
+ newsize = offset + len;
+ isize = i_size_read(inode);
+
+ if (mode & FALLOC_FL_ZERO_RANGE) {
+ struct exfat_inode_info *ei = EXFAT_I(inode);
+ loff_t saved_validsize = ei->valid_size;
+
+ /* The requested range must span to or past EOF */
+ if (newsize < isize) {
+ err = -EOPNOTSUPP;
+ goto error;
+ }
+
+ /* valid_size can only be truncated */
+ if (offset < ei->valid_size)
+ ei->valid_size = offset;
+ /* If offset >= ei->valid_size, the range is already zeroed so that'd be no-op */
+
+ if (!(mode & FALLOC_FL_KEEP_SIZE) && isize < newsize)
+ err = exfat_cont_expand(inode, newsize);
+ /* inode invalidated in exfat_cont_expand() */
+ else {
+ /* update inode */
+ inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
+ mark_inode_dirty(inode);
+
+ if (IS_SYNC(inode))
+ err = write_inode_now(inode, 1);
+ }
+
+ if (err) {
+ /* inode unchanged - revert valid_size */
+ ei->valid_size = saved_validsize;
+ goto error;
+ }
+
+ /* drop cache after the new valid_size */
+ if (ei->valid_size != saved_validsize)
+ truncate_pagecache(inode, ei->valid_size);
+ } else { /* mode == FALLOC_FL_ALLOCATE_RANGE */
+ if (newsize <= isize)
+ goto error;
- /* This is just an expanding truncate */
- err = exfat_cont_expand(inode, newsize);
+ /* This is just an expanding truncate */
+ err = exfat_cont_expand(inode, newsize);
+ }
error:
inode_unlock(inode);
^ permalink raw reply related [flat|nested] 3+ messages in thread