On 1/25/21 4:43 PM, Kevin Wolf wrote: > Am 25.01.2021 um 16:05 hat Philippe Mathieu-Daudé geschrieben: >> Is it possible to restrict a block driver to a particular set of >> options? In my case I'd like to restrict the raw driver to regular files. >> >> I noticed the NFS driver does it locally in nfs_client_open(), >> and FUSE has is_regular_file() -- which is POSIX specific however. >> >> When a backend is a SCSI drive, the block layer provide the blk_is_sg() >> method to test it. >> 1/ Should I provide a similar blk_is_regular_file()? >> >> 2/ There is no oslib function to check for regular file, >> should I add one too? > > I find this question confusing because on one hand you're talking about > block driver implementations like NFS, but on the other hand about SCSI > devices, which are users, not implementations of block drivers.
Sorry for the confusion and thanks for the quick answer :) My question is confused because the problem is not clear to me... > At which level is the code where you think you need to make this > distinction? (see below) > The other problem is that "is this a regular file?" is probably not what > you're really interested in. The content of an image can be spread > across several files (for example, consider backing files) or not use a > local file descriptor at all (network protocol drivers), and block layer > functions should ideally make sense for all drivers unless something can > only possibly make sense for a single driver (blk_is_sg might be a case > of this). > > I assume that you are interested in some specific property that regular > files happen to provide. If at all possible, we shouldn't check for a > specific backend type, but for capabilities or properties of a given > block node. > > So what are you really trying to do here? Well, maybe this is more an emulation problem rather than a block one. But system emulation consumes block layer :) The problem is when emulating devices such NOR Flash (parallel mapping or SD cards) we expect the block driver being a plain file (either "raw" format or another) but a "regular" file. When an user passes something else like a block device, odd things happen. Well, I guess I self-restricted my question to device emulation. So in the cases mentioned I would like to add a check in sd_realize()/ pflash_cfi0?_realize() for regular file when a block drive is provided. Description of problematic user case: * -pflash /dev/sda * -sd /dev/mmcblk0 User runs emulation on top of hardware (maybe like passthru?), and expect underlying block to be in correct state out of QEMU. Thanks, Phil.
