RE: [PATCH] hfsplus: limit sb_maxbytes to partition size

[Viacheslav Dubeyko]

On Fri, 2026-03-06 at 09:57 +0900, Hyunchul Lee wrote:
> On Thu, Mar 05, 2026 at 11:21:19PM +0000, Viacheslav Dubeyko wrote:
> > On Thu, 2026-03-05 at 10:52 +0900, Hyunchul Lee wrote:
> > > > > 
> > > > > Sorry it's generic/285, not generic/268.
> > > > > in generic/285, there is a test that creates a hole exceeding the block
> > > > > size and appends small data to the file. hfsplus fails because it fills
> > > > > the block device and returns ENOSPC. However if it returns EFBIG
> > > > > instead, the test is skipped.
> > > > > 
> > > > > For writes like xfs_io -c "pwrite 8t 512", should fops->write_iter
> > > > > returns ENOSPC, or would it be better to return EFBIG?
> > > > > > 
> > > > 
> > > > Current hfsplus_file_extend() implementation doesn't support holes. I assume you
> > > > mean this code [1]:
> > > > 
> > > >         len = hip->clump_blocks;
> > > >         start = hfsplus_block_allocate(sb, sbi->total_blocks, goal, &len);
> > > >         if (start >= sbi->total_blocks) {
> > > >                 start = hfsplus_block_allocate(sb, goal, 0, &len);
> > > >                 if (start >= goal) {
> > > >                         res = -ENOSPC;
> > > >                         goto out;
> > > >                 }
> > > >         }
> > > > 
> > > > Am I correct?
> > > > 
> > > Yes,
> > > 
> > > hfsplus_write_begin()
> > >   cont_write_begin()
> > >     cont_expand_zero()
> > > 
> > > 1) xfs_io -c "pwrite 8t 512"
> > > 2) hfsplus_begin_write() is called with offset 2^43 and length 512
> > > 3) cont_expand_zero() allocates and zeroes out one block repeatedly
> > > for the range
> > > 0 to 2^43 - 1. To achieve this, hfsplus_write_begin() is called repeatedly.
> > > 4) hfsplus_write_begin() allocates one block through hfsplus_get_block() =>
> > > hfsplus_file_extend()
> > 
> > I think we can consider these directions:
> > 
> > (1) Currently, HFS+ code doesn't support holes. So, it means that
> > hfsplus_write_begin() can check pos variable and i_size_read(inode). If pos is
> > bigger than i_size_read(inode), then hfsplus_file_extend() will reject such
> > request. So, we can return error code (probably, -EFBIG) for this case without
> > calling hfsplus_file_extend(). But, from another point of view, maybe,
> > hfsplus_file_extend() could be one place for this check. Does it make sense?
> > 
> > (2) I think that hfsplus_file_extend() could treat hole or absence of free
> > blocks like -ENOSPC. Probably, we can change the error code from -ENOSPC to -
> > EFBIG in hfsplus_write_begin(). What do you think?
> > 
> Even if holes are not supported, shouldn't the following writes be
> supported?
> 
> xfs_io -f -c "pwrite 4k 512" <file-path>
> 
> If so, since we need to support cases where pos > i_size_read(inode),

The pos > i_size_read(inode) means that you create the hole. Because,
oppositely, when HFS+ logic tries to allocate new block, then it expects to have
pos == i_size_read(inode). And we need to take into account this code [1]:

	if (iblock >= hip->fs_blocks) {
		if (!create)
			return 0;
		if (iblock > hip->fs_blocks) <-- This is the rejection of hole
			return -EIO;
		if (ablock >= hip->alloc_blocks) {
			res = hfsplus_file_extend(inode, false);
			if (res)
				return res;
		}
	}

The generic_write_end() changes the inode size: i_size_write(inode, pos +
copied).

> wouldn't the condition "pos - i_size_read(inode) > free space" be better?
> Also instead of checking every time in hfsplus_write_begin() or
> hfsplus_file_extend(), how about implementing the check in the
> file_operations->write_iter callback function, and returing EFBIG?

Which callback do you mean here? I am not sure that it's good idea.

Thanks,
Slava.

> 
> > > 
> > > 

[1] https://elixir.bootlin.com/linux/v6.19/source/fs/hfsplus/extents.c#L239