[Ecls-list] directory function and stat system calls

[Juan Jose Garcia-Ripoll]

On Fri, Dec 18, 2009 at 8:01 AM, Robert Dodier <robert.dodier at gmail.com>wrote:

> On 12/17/09, Juan Jose Garcia-Ripoll
> <juanjose.garciaripoll at googlemail.com> wrote:
> > On Wed, Dec 16, 2009 at 6:14 AM, Robert Dodier
>
> > An unfortunate mistake: DIRECTORY used stat() on all entries in a
> directory,
> > not only those that matched the mask. It was just a matter of switching
> > lines. Now things are better. Thanks a lot for reporting.
>
> > $ echo '(directory "/Users/jjgarcia/tmp/")(quit)' > foo.lsp; sudo dtrace
> -n
> > 'pid$target::safe_stat:entry  { printf("%s\n",
> copyinstr((uintptr_t)arg0));
> > }' -c "ecl -norc -load foo"
> > dtrace: description 'pid$target::safe_stat:entry  ' matched 1 probe
> > ;;; Loading #P"/Users/jjgarcia/foo.lsp"
> > dtrace: pid 39532 has exited
> > CPU     ID                    FUNCTION:NAME
> >   0  19180                  safe_stat:entry jjgarcia
> >   0  19180                  safe_stat:entry tmp
>
> Hmm. I updated from CVS and I got r1.100 src/d/unixfsys.d
> which has the modified code. I did a clean build,
> but I get the same behavior as before.
>

No, you are not seeing the same behavior as before. Before, if ECL wanted to
list a directory of /var/tmp/foo/a.txt it would run through the directory
chain "stat-ing" the content of /var, /tmp and /foo Now it only does what is
expected: it lists the content of each directory, and only inspect those
that match the masks "var", "tmp", "foo" and "a.txt" There are thus only a
few calls to "stat" which HAVE to be done: "var", "tmp", "foo" have to be
verified not to be files, and for "a.txt" we have to verify it is not a
symbolic link or return its true name.

Before thet patch

$ trace ecl -eval '(directory "/home/jjgarcia/mtp/foo")' -eval '(quit)' 2>&1
|tee ~/log
$ grep stat log |wc -l
162

After the patch

$ trace ecl -eval '(directory "/home/jjgarcia/mtp/foo")' -eval '(quit)' 2>&1
|tee ~/log2
$ grep stat log2 |wc -l
64

More precisely

[... stat due to system loading libraries ...]
fstat(4, {st_mode=S_IFREG|0755, st_size=411898, ...}) = 0
lstat("/home/jjgarcia/", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
stat("home", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
stat("jjgarcia", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
stat("mtp", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
stat("foo", {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
lstat("foo", {st_mode=S_IFREG|0644, st_size=0, ...}) = 0



> For the record, I'm looking at the output of strace,
> not dtrace, which appears to be something else.
>

There is no strace in OS X. dtrace does the same and more: it allows you to
select which calls to log. But I used "strace" in another box to show this
works.


> I don't know what safe_stat is; I'm guessing it is a library
> function instead of a system call and, therefore,
> not immediately relevant. (I'm interested in the calls to stat64.)


Please do not assume I am a fool by default. safe_stat() is a wrapper around
stat() that captures any error condition, similarly there is safe_lstat()
and other wrappers.

Juanjo

-- 
Instituto de Física Fundamental, CSIC
c/ Serrano, 113b, Madrid 28006 (Spain)
http://juanjose.garciaripoll.googlepages.com
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