site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com On Mar 7, 2007, at 3:45 AM, Anton Altaparmakov wrote: [ ... ] -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... /* Create a page list for the wanted page. */ kerr = ubc_create_upl(ni->vn, ofs, PAGE_SIZE, upl, pl, UPL_SET_LITE | (rw ? UPL_WILL_MODIFY : 0)); if (kerr != KERN_SUCCESS) panic("%s(): Failed to get page (error %d).\n", __FUNCTION__, (int)kerr); /* * If the page is not valid, need to read it in from the vnode now thus * making it valid. */ if (!upl_valid_page(*pl, 0)) { ntfs_debug("Reading page as it was not valid."); err = ntfs_pagein(ni, ofs, PAGE_SIZE, *upl, 0, UPL_IOSYNC | UPL_NOCOMMIT); if (err) { ntfs_error(ni->vol->mp, "Failed to read page (error " "%d).", err); goto pagein_err; } } /* Map the page into the kernel's address space. */ kerr = ubc_upl_map(*upl, (vm_offset_t*)kaddr); if (kerr == KERN_SUCCESS) { ntfs_debug("Done."); return 0; } ntfs_error(ni->vol->mp, "Failed to map page (error %d).", (int)kerr); err = EIO; I may be misunderstanding the simplification you performed, and if so, forgive me... You want to call ubc_upl_map() before you do the I/O, or the UPL could have been recycled while the system was under extreme pressure, which would result in it being thrown away before a mapping was established to hold it in place. It looks like the failure mode in this case would cause a ""Failed to map page" message if debugging was on, and an EIO, which I suspect would not be re-driven down. Even if the EIO caused to to be redriven down instead of returning an error up the stack, potentially to the program on the other end of a system call, you might still not be very happy, if the system stays under pressure, since it can happen repeatedly, if the load is sustained. You probably want to look to bsd/vfs/vfs_bio.c and how HFS does things for your example (e.g. the usage of ubc_upl_map() in buf_map() & company). You probably also want to drive the I/O through the fault on access, through the page-in path, rather than an explicit I/O through ntfs_pagein(). The reason the cd9660 code does it the other way is because CD's don't have normal page-aligned block boundaries, so avoiding the direct I/O and letting the VM system schedule instead could be inefficient. This email sent to site_archiver@lists.apple.com