On Thu, Feb 22, 2018 at 06:11:14AM +0000, Luck, Tony wrote: >> On Feb 21, 2018, at 21:52, Linus Torvalds wrote: >> >> Does the error return actually break real users? Not "I can do did >> things and it acts differently" things, but actual users... > > Probably not. Peter Jones said that efibootmgr might access up to 20 > files. Assuming it is sanely reading in big chunks, it won’t hit the > rate limit that I set at 100.
Typically each read looks like: openat(AT_FDCWD, "/sys/firmware/efi/efivars/Boot0001-8be4df61-93ca-11d2-aa0d-00e098032b8c", O_RDONLY) = 3 read(3, "\7\0\0\0", 4) = 4 read(3, "\1\0\0\0b\0t\0e\0s\0t\0\0\0\4\1*\0\1\0\0\0\0\10\0\0\0\0\0\0"..., 4096) = 114 read(3, "", 3982) = 0 close(3) = 0 For each multiple of 4k, you'll see one more read() call. (It's two reads because libefivar's efi_get_variable() returns the attributes separately from the data, which goes in an allocation the caller is responsible for freeing, so doing it as one read means it would introduce an extra copy.) Looking at that code path, if it *does* get tripped up by EAGAIN, it should handle it fine, though maybe I should add a short randomized delay (or just sched_yield()) in that case. I don't think the 3rd read there to detect EOF hits the efivarfs code, so that's 2 reads per variable until you go over 4k, which most never do. That pattern is true of everything that uses libefivar to do its EFI variable manipulation. On my moderately typical laptop with 2 boot variables set, it looks something like: trillian:~$ strace -o efibootmgr.strace efibootmgr -v BootCurrent: 0001 Timeout: 0 seconds BootOrder: 0001,0000 Boot0000* Fedora HD(1,GPT,2cf5261b-7b98-48c0-ae54-463dbd23e65b,0x800,0x64000)/File(\EFI\fedora\shimx64.efi) Boot0001* test HD(1,GPT,2cf5261b-7b98-48c0-ae54-463dbd23e65b,0x800,0x64000)/File(\EFI\fedora\shimx64.efi) trillian:~$ grep '^\(open\|read\)' efibootmgr.strace | grep -A100 sys/firmware | grep -c ^read 15 Which, if I'm write about VFS eating that last read, means 10 calls. Many machines have some default boot variables; my desktop at home has 5 completely useless variables the firmware sets. So there it winds up being 27 calls to read(2), and thus 18 calls to count towards our limit. Your limit at 100 looks sufficiently large to me. -- Peter -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html