On Mon, 14 Feb 2022 17:43:51 +0300 Vitaly Chikunov <v...@altlinux.org> wrote:
> Christian, > > On Mon, Feb 14, 2022 at 12:44:48PM +0100, Christian Schoenebeck wrote: > > On Montag, 14. Februar 2022 11:36:53 CET Greg Kurz wrote: > > > The synth backend should be fixed to honor d_reclen, or > > > at least to allocate with g_new0(). > > > > Yes, I overlooked that this is not initialized with zero already. > > > > With g_new0() d_reclen would be zero and qemu_dirent_dup() would then > > fallback > > to the portable branch (as I assumed it already would): > > Perhaps, this additional change should be added (I only found two instances of > V9fsSynthOpenState allocation): > > diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c > --- a/hw/9pfs/9p-synth.c > +++ b/hw/9pfs/9p-synth.c > @@ -182,7 +182,7 @@ static int synth_opendir(FsContext *ctx, > V9fsSynthOpenState *synth_open; > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > - synth_open = g_malloc(sizeof(*synth_open)); > + synth_open = g_malloc0(sizeof(*synth_open)); > synth_open->node = node; > node->open_count++; > fs->private = synth_open; > @@ -266,7 +266,7 @@ static int synth_open(FsContext *ctx, V9fsPath *fs_path, > V9fsSynthOpenState *synth_open; > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > - synth_open = g_malloc(sizeof(*synth_open)); > + synth_open = g_malloc0(sizeof(*synth_open)); > synth_open->node = node; > node->open_count++; > fs->private = synth_open; > > > Additionally I would add NAME_MAX to the V9fsSynthOpenState allocation > > size, > > because it is known that some systems define dirent as flex-array (zero > > d_name > > size). > > (To be precise) not just zero, but 1 byte. Also, to remind, for some > filesystems, such as CIFS, actual d_name size could be longer than NAME_MAX. > Because of that struct dirent cannot be allocated statically or with simple > sizeof. > > > > > I know Greg would not favour this solution (using g_new0), but it's the > > most > > minimalistic and most portable solution. So I would favour it for now. > > Why g_new0 and not just g_malloc0? This is smallest code change, which seems > appropriate for a bug fix. > I prefer g_new0() for the exact reasons that are provided in QEMU's official coding style docs/devel/style.rst: --- Prefer ``g_new(T, n)`` instead of ``g_malloc(sizeof(T) * n)`` for the following reasons: * It catches multiplication overflowing size_t; * It returns T ``*`` instead of void ``*``, letting compiler catch more type errors. Declarations like .. code-block:: c T *v = g_malloc(sizeof(*v)) are acceptable, though. --- I'm fine with the acceptable version as well. The only important thing is to fix the synth backend. Cheers, -- Greg > Thanks, > > > > > A cleaner solution on the long-term would be turning V9fsSynthOpenState's > > 'dent' member into a pointer and adding a new function to osdep like: > > > > struct dirent * > > qemu_dirent_new(const char* name) { > > ... > > } > > > > But I would like to postpone that qemu_dirent_new() solution, e.g. because > > I > > guess some people would probably not like qemu_dirent_new() to have in > > osdep, > > as it is probably not a general purpose function, and I am not keen putting > > qemu_dirent_new() into a different location than qemu_dirent_dup(), because > > it > > would raise the danger that system dependent code might deviate in future. > > > > Best regards, > > Christian Schoenebeck > >