Change Details

Currently only vnodes and devices are eligible for linux mmap, but shmfd (shm_open/memfd_create) should also be allowed.

Linux mmap rejects mmap() on a write-only file with EACCES. linux_mmap_common currently does a fun dance to grab the fp associated with the passed in fd, validates it, then drops the reference and calls into kern_mmap(). Doing so is perhaps both fragile and premature; there's still plenty of chance for the request to get rejected with a more appropriate error. This change alleviates the need to do this by providing a kern_mmap variant that allows the caller to inspect the fp just before calling into the fileop layer. The callback takes flags, prot, and maxprot as one could imagine scenarios where any of these, in conjunction with the file itself, may influence a caller's decision.

Currently only vnodes and devices are eligible for linux mmapLinux mmap rejects mmap() on a write-only file with EACCES. linux_mmap_common currently does a fun dance to grab the fp associated with the passed in fd, validates it, then drops the reference and calls into kern_mmap(). Doing so is perhaps both fragile and premature; there's still plenty of chance for the request to get rejected with a more appropriate error. This change alleviates the need to do this by providing a kern_mmap variant that allows the caller to inspect the fp just before calling into the fileop layer. The callback takes flags, prot, and maxprot as one could imagine scenarios where any of these, but shmfd (shm_open/memfd_create) should also be allowed.in conjunction with the file itself, may influence a caller's decision.