Re: [PATCH v5 33/40] netfs, cachefiles: Pass upper bound length to allow expansion

David Howells
2024-01-02T17:11:28Z

Gao Xiang <hsiangkao@linux.alibaba.com> wrote:

> > down = start - round_down(start, PAGE_SIZE);
> > *_start = start - down;
> > *_len = round_up(down + len, PAGE_SIZE);
> > + if (down < start || *_len > upper_len)
> > + return -ENOBUFS;
>
> Sorry for bothering. We just found some strange when testing
> today-next EROFS over fscache.
>
> I'm not sure the meaning of
> if (down < start
>
> For example, if start is page-aligned, down == 0.
>
> so as long as start > 0 and page-aligned, it will return
> -ENOBUFS. Does it an intended behavior?

Yeah, I think that's wrong.

Does the attached help?

David
---

diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index bffffedce4a9..7529b40bc95a 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -522,16 +522,22 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
bool no_space_allocated_yet)
{
struct cachefiles_cache *cache = object->volume->cache;
- loff_t start = *_start, pos;
- size_t len = *_len, down;
+ unsigned long long start = *_start, pos;
+ size_t len = *_len;
int ret;

/* Round to DIO size */
- down = start - round_down(start, PAGE_SIZE);
- *_start = start - down;
- *_len = round_up(down + len, PAGE_SIZE);
- if (down < start || *_len > upper_len)
+ start = round_down(*_start, PAGE_SIZE);
+ if (start != *_start) {
+ kleave(" = -ENOBUFS [down]");
+ return -ENOBUFS;
+ }
+ if (*_len > upper_len) {
+ kleave(" = -ENOBUFS [up]");
return -ENOBUFS;
+ }
+
+ *_len = round_up(len, PAGE_SIZE);

/* We need to work out whether there's sufficient disk space to perform
* the write - but we can skip that check if we have space already
@@ -542,7 +548,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,

pos = cachefiles_inject_read_error();
if (pos == 0)
- pos = vfs_llseek(file, *_start, SEEK_DATA);
+ pos = vfs_llseek(file, start, SEEK_DATA);
if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {
if (pos == -ENXIO)
goto check_space; /* Unallocated tail */
@@ -550,7 +556,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
cachefiles_trace_seek_error);
return pos;
}
- if ((u64)pos >= (u64)*_start + *_len)
+ if (pos >= start + *_len)
goto check_space; /* Unallocated region */

/* We have a block that's at least partially filled - if we're low on
@@ -563,13 +569,13 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,

pos = cachefiles_inject_read_error();
if (pos == 0)
- pos = vfs_llseek(file, *_start, SEEK_HOLE);
+ pos = vfs_llseek(file, start, SEEK_HOLE);
if (pos < 0 && pos >= (loff_t)-MAX_ERRNO) {
trace_cachefiles_io_error(object, file_inode(file), pos,
cachefiles_trace_seek_error);
return pos;
}
- if ((u64)pos >= (u64)*_start + *_len)
+ if (pos >= start + *_len)
return 0; /* Fully allocated */

/* Partially allocated, but insufficient space: cull. */
@@ -577,7 +583,7 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
ret = cachefiles_inject_remove_error();
if (ret == 0)
ret = vfs_fallocate(file, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
- *_start, *_len);
+ start, *_len);
if (ret < 0) {
trace_cachefiles_io_error(object, file_inode(file), ret,
cachefiles_trace_fallocate_error);