[I already typed this once but lost power before sending. :-(
This time, I ensured auto-save-mode is on.]
Paul Eggert <[EMAIL PROTECTED]> writes:
> What does 'ls -l' do? Users will probably want 'tar' to do something similar.
It starts the passive translator and gets the stat data from
that. This makes the first run of 'ls -l /dev' or even 'ls
--color /dev' very slow.
> What 'ls' switch is used to see a translator rather than to invoke it?
> What does the 'ls' output look like in that case?
There is no such switch, but there is a separate program
'showtrans'. I can't test now, but if I read the source right,
the output of 'showtrans /etc/passwd /dev/full' would look like:
/etc/passwd
/dev/full: /hurd/null --full
This means /etc/passwd has no translator, and /dev/full has
"/hurd/null" with an argument of "--full". These strings are
internally kept null-terminated, so they could contain spaces,
but the output of showtrans is ambiguous if they do.
There has been a lot of talk about extending 'ls' to display the
Hurd's fourth rwx permission set. When someone eventually does
that, (s)he could also add an option for showing passive
translators. That would be more convenient than a separate
'showtrans' program, I think. The output could then also obey
the '--quoting-style' option.
When 'tar' saves a translator, it must also save the file or
directory underlying the translator, in case the translator wants
to access it when run. The underlying node can be opened with
O_NOTRANS.
The tar format should be extended to support the following data
for each file, in addition to what it stores already:
1. Passive translator.
Usage: Command line for a program that the parent filesystem
starts when a process looks up the file.
Type: List of strings. The strings cannot contain null
characters.
Frequency: Most files haven't got passive translators.
Format: The RPC interfaces and ext2fs (I don't know about
ufs) keep the passive translator in argz format (see the glibc
manual) so it could be easiest to use that format in the tar
file too. The ext2fs format restricts the argz to the
filesystem block length minus two bytes, but I don't think tar
should inherit that limitation.
Default: When extracting a non-Hurd archive, don't set a
translator except implicitly via mknod or symlink.
API: There is S_IPTRANS for mode_t, but I think that's a bit
late since a stat already uses the translator. 'showtrans'
gets a Mach port to the file with file_name_lookup, reads the
passive-translator argz with file_get_translator, and closes
the port with mach_port_deallocate. 'settrans' uses
file_set_translator in a similar way.
2. Fourth rwx set.
Usage: Read, Write and Execute permissions for processes that
don't have any UIDs at all. There is also a bit that says
whether the fourth set is active. If it is not active, then
the "other" set is used instead. Legacy programs that set
permissions are expected to store 0 in the activity bit, which
currently means "not active". Some later version of the Hurd
may change 0 to mean "active", so that UIDless processes
don't get any permissions by default (since the rwx bits are
also 000).
Type: 3+1 bits.
Frequency: In principle, all files have these bits. However,
they will often be all zero.
Format: If the bits are zero, I think they needn't be saved.
The possible future inversion of the activity bit could
corrupt permissions of old tar files. I think it is best to
only design the format for now and not actually save nonzero
values until we know for sure whether the bit will be
inverted.
Default: Zero. If it's good enough for legacy programs, it's
good enough for legacy archives.
API: These mode_t bits can be read with stat and changed with
chmod. Constants: S_IUSEUNK, S_IUNKNOWN, S_IUNKSHIFT. See
<bits/stat.h> for details.
3. Author ID.
Usage: Another UID. Doesn't affect any permissions. The
owner or root can store any value here.
Type: uid_t, 32 bits.
Frequency: All files have an author ID, but it is normally
the same as the owner UID.
Format: I suppose tar could store both the number and the
name, like with UID and GID.
Default: When extracting a non-Hurd archive, don't set the
author ID; let the file system choose the default.
(FIXME: Is this reasonable if 'tar' then does a chown?)
API: To read the author ID, use stat and see st_author. To
change it, get a Mach port to the file and call file_chauthor.
Can these be added in such a way that older tars can still read
Hurd tar archives?
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