On Sat, Jan 23, 2021 at 11:22:13PM +0800, Gao Xiang wrote: > On Sat, Jan 23, 2021 at 09:18:30PM +0800, 胡玮文 wrote: > > On Fri, Jan 22, 2021 at 09:49:01AM +0800, Gao Xiang wrote: > > > Hi Weiwen, > > > > > > On Fri, Jan 22, 2021 at 09:00:44AM +0800, 胡玮文 wrote: > > > > Hi Xiang, > > > > > > > > > 在 2021年1月22日，08:34，Gao Xiang <hsiang...@redhat.com> 写道： > > > > > > > > > > Hi Weiwen, > > > > > > > > > >> On Fri, Jan 22, 2021 at 12:31:43AM +0800, Hu Weiwen wrote: > > > > >> readlink should fill a **null terminated** string in buffer. > > > > >> > > > > >> Also, read should return number of bytes remaining on EOF. > > > > >> > > > > >> Link: > > > > >> https://lore.kernel.org/linux-erofs/20210121101233.gc6...@desktop-n4cecto.huww98.cn/ > > > > >> Signed-off-by: Hu Weiwen <seh...@mail.scut.edu.cn> > > > > > > > > > > Thanks for catching this! > > > > > > > > > >> --- > > > > >> fuse/main.c | 14 +++++++++++++- > > > > >> 1 file changed, 13 insertions(+), 1 deletion(-) > > > > >> > > > > >> diff --git a/fuse/main.c b/fuse/main.c > > > > >> index c162912..bc1e496 100644 > > > > >> --- a/fuse/main.c > > > > >> +++ b/fuse/main.c > > > > >> @@ -71,6 +71,12 @@ static int erofsfuse_read(const char *path, char > > > > >> *buffer, > > > > >> if (ret) > > > > >> return ret; > > > > >> > > > > >> + if (offset >= vi.i_size) > > > > >> + return 0; > > > > >> + > > > > >> + if (offset + size > vi.i_size) > > > > >> + size = vi.i_size - offset; > > > > >> + > > > > > > > > > > It would be better to call erofs_pread() with the original offset > > > > > and size (also I think there is some missing memset(0) for > > > > > !EROFS_MAP_MAPPED), and fix up the return value to the needed value. > > > > > > > > Yes, that is what I have initially tried. But this way is harder than I > > > > thought. > > > > EROFS_MAP_MAPPED flag seems to be designed to handle sparse file, and > > > > is reused to > > > > represent EOF. So maybe we need a new flag to represent EOF? > > > > > > Nope, I think we just need to handle return value of read, I mean > > > > > > erofs_ilookup() > > > > > > ret = erofs_pread() > > > if (ret) > > > return ret; > > > > > > if (offset + size > vi.i_size) > > > return vi.i_size - offset; > > > > > > return size; > > > > > > Is that enough? Am I missing something? > > > > This should work, except we should also add this branch > > > > if (offset >= vi.i_size) > > return 0; > > yeah, agreed. It'd also be added after erofs_pread(). > > > > > But how this is better than my original patch? I would say my patch should > > be > > more efficient. > > > > By saying "what I have initially tried" in my last mail, I mean changing > > erofs_pread() to return the number of bytes read (just like pread system > > call, > > instead of always 0). I think this is easier to understand for others, but > > seems harder to implement. Do you think this is worthful? > > > > There are 2 reasons for me to do it at least: > 1) need to memset(0) for these unmapped buffers; > 2) introduce a hook to fs to read data regardless of i_size, > just as linux kernel page cache approach. > > Don't be confused with ->i_size (this is only a EOF-marker) and > the real inode data, that are two different concepts for me, I'd > like to handle all data processing in erofs_pread() (even for > post-EOF case), but only deal with i_size in erofsfuse_read(). >
Also, no need to follow erofs_pread() as the pread() system call. It just used a similiar name. The core concept of this is to handle file data itself. There is nothing to do with eof-marker (but much related to inode extent/block mapping instead, although currently EROFS extent mapping format internally relies on i_size.) Thanks, Gao Xiang > Thanks, > Gao Xiang >
