service_solahart_jakarta_selatan__082122541663/git_nfs_mmap.mdwn


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55

[[!meta copyright="Copyright © 2011, 2012 Free Software Foundation, Inc."]]

[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
id="license" text="Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license
is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]

[[!tag open_issue_porting]]

    $ git-new-workdir /media/kepler-data/home/thomas/tmp/source/binutils/git master master
    fatal: Out of memory? mmap failed: No such device
    $ echo $?
    128
    $ showtrans /media/kepler-data
    /hurd/nfs kepler.schwinge.homeip.net:/media/data

With `sh -x`:

    [...]
    + ln -s /media/kepler-data/home/thomas/tmp/source/binutils/git/.git/remotes master/.git/remotes
    + ln -s /media/kepler-data/home/thomas/tmp/source/binutils/git/.git/rr-cache master/.git/rr-cache
    + ln -s /media/kepler-data/home/thomas/tmp/source/binutils/git/.git/svn master/.git/svn
    + cd master
    + cp /media/kepler-data/home/thomas/tmp/source/binutils/git/.git/HEAD .git/HEAD
    + git checkout -f master
    fatal: Out of memory? mmap failed: No such device

As one can easily guess (and confirm with [[hurd/debugging/rpctrace]]), `git`
tries to [[glibc/mmap]] a file via the [[hurd/translator/nfs]] translator, this
fails, and it isn't prepared to cope with that:

    [...]
      88->dir_lookup (".git/objects/pack/pack-37ca560e7877fa0cc6e5ddcd556aa73e5a3e3f40.idx" 2049 0) = 0 3 "/media/kepler-data/home/thomas/tmp/source/binutils/git/.git/objects/pack/pack-37"  (null)
      62->dir_lookup ("media/kepler-data/home/thomas/tmp/source/binutils/git/.git/objects/pack/pack-37c" 2049 0) = 0 1 "/home/thomas/tmp/source/binutils/git/.git/objects/pack/pack-37ca560e7877fa0cc6e5"   61
      61->dir_lookup ("home/thomas/tmp/source/binutils/git/.git/objects/pack/pack-37ca560e7877fa0cc6e5d" 2049 0) = 0 1 ""   84
    task3741-> 3206 (pn{ 33}) = 0
      84->term_getctty () = 0xfffffed1 ((ipc/mig) bad request message ID)
      84->io_stat_request () = 0 {1 704 0 36308992 0 0 -1 33060 1 1000 1000 4712 0 1307711395 0 1307657003 0 1307657003 0 4096 16 0 1000 0 0 100663296 1836017780 29537 0 0 0 0}
      84->io_map_request () = 0x4000002d (Operation not supported)
      84->io_map_request () = 0x4000002d (Operation not supported)
      76->io_write_request ("fatal: Out of memory? mmap failed: No such device
    " -1) = 0 50
      64->proc_mark_exit_request (32768 0) = 0
    task3741-> 2008 () = 0
    Child 3741 exited with 128

This is the [[libnetfs: `io_map`|service_solahart_jakarta_selatan__082122541663/libnetfs_io_map]] issue.

There is a `NO_MMAP` conditional in Git's source code, but it is a compile-time
conditional.  The fallback code in `compat/mmap.c:git_mmap` only supports
`MAP_PRIVATE`, and simply `pread`s in the requested portion of a file.  This
could be made a runtime fallback, too.