On Mon, Mar 21, 2016 at 6:28 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Thu, Mar 17, 2016 at 10:02:00AM +0100, Miklos Szeredi wrote: >> Add a new helper, file_dentry() [*], to get the filesystem's own dentry >> from the file. This simply compares file_inode(file->f_path.dentry) to >> file_inode(file) and if they are equal returns file->f_path.dentry (this is >> the common, non-overlayfs case). >> >> In the uncommon case (regular file on overlayfs) it will call into >> overlayfs's ->d_native_dentry() to get the underlying dentry matching >> file_inode(file). > > What's wrong with making ovl_dentry_real() an instance of optional > ->d_real() method and having a flag (DCACHE_OP_REAL) controlling its > calls? With d_real(dentry) returning either that or dentry itself, > and file_dentry(file) being simply d_real(file->f_path.dentry)... > > Why do we need to look at the inode at all? d_set_d_op() dereferences > ->d_op anyway, as well as setting ->d_flags, so there's no extra cost > there, and "test bit in ->d_flags + branch not taken" is all it would > cost in normal case... Checking DCACHE_OP_REAL insted of inode would be fine. But d_real() needs inode as well. Consider the case where 1) file opened on lower layer 2) copied up 3) file_dentry() called d_real(file->f_path.dentry) would return the upper dentry but that's not what we want. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
