Forgive me for posting this verbatim from a thread on another forum; and for it sounding a lot like a Linux issue- its not:

As the post suggests, I'm having some issues with Fuse and perl, namely the write_buffer size. Now, this could just be a Fuse issue, and if it is I'd ask a mod to remove this, but I don't think it is.

The background;
Firstly, my implementation is working, and working well. I'm getting reasonable consistency in my read/writes, even with different sizes, and so I'm pretty sure my perl is working well (Which is why I haven't posted any of it, though I can if you need).

I've implemented a very simple, bog standard filesystem with hashrefs, and similar data structures, all looks good. The problem is that the writes are being done in 4096 blocks; the Fuse standard.

Because this is the fuse standard, I did a grep for the write size: 

root@jcmain:~# !1810
grep -inH max_write `locate fuse` 2>/dev/null
/usr/include/fuse/fuse_common.h:105:    unsigned max_write;
/usr/include/linux/fuse.h:363:  __u32   max_write;
.....snip.....
/usr/src/linux-2.6.30-custom/fs/fuse/file.c:786:                bytes 
+= min_t(size_t, bytes, fc->max_write - count);
/usr/src/linux-2.6.30-custom/fs/fuse/file.c:823:        } while (iov_i
+ter_count(ii) && count < fc->max_write &&
/usr/src/linux-2.6.30-custom/fs/fuse/file.c:987:        size_t nmax = 
+write ? fc->max_write : fc->max_read;
/usr/src/linux-2.6.30-custom/fs/fuse/fuse_i.h:322:      unsigned max_w
+rite;
/usr/src/linux-2.6.30-custom/fs/fuse/inode.c:763:               fc->ma
+x_write = arg->minor < 5 ? 4096 : arg->max_write;
/usr/src/linux-2.6.30-custom/fs/fuse/inode.c:764:               fc->ma
+x_write = max_t(unsigned, 4096, fc->max_write);
/usr/src/linux-2.6.30-custom/include/linux/fuse.h:401:  __u32   max_wr
+ite;
.....snip.....
root@jcmain:~# uname -a
Linux jcmain 2.6.30-custom #1 SMP Fri Jun 12 22:15:25 BST 2009 i686 GN
+U/Linux

[download]

and found the module which referenced 4096 on my kernel; /usr/src/linux-2.6.30-custom/fs/fuse/inode.c
I changed 4096 to 131072 (I forget why that number, I think I saw it somewhere whilst researching this, but no idea where/why), recompiled the module, unloaded the old fuse module and loaded this one. I was even convinced it'd worked:

jc@jcmain:~/steg$ sudo perl fs_simple.pl 
unique: 1, opcode: INIT (26), nodeid: 0, insize: 56
INIT: 7.11
flags=0x0000003b
max_readahead=0x00020000
   INIT: 7.8
   flags=0x00000000
   max_readahead=0x00020000
   max_write=0x00020000
   unique: 1, error: 0 (Success), outsize: 40

[download]
0x00020000 being: 
jc@jcmain:~$ perl -e "print int 0x00020000;"
131072

[download]

Which tells me that perl it's self has set the 4096 from somewhere else. Its not, however, built into Fuse.pm or Fuse::Simple.pm - which is what I'm using:

jc@jcmain:/usr/lib/perl5$ grep 4096 Fuse.pm 
jc@jcmain:/usr/lib/perl5$ 
<snip>
jc@jcmain:/usr/local/share/perl/5.10.0/Fuse$ grep 4096 Simple.pm 
jc@jcmain:/usr/local/share/perl/5.10.0/Fuse$

[download]

So what am I missing? Does anyone remember solving the same sort of problem? Can it be solved? Is it even considered a problem, more a feature?

Hell, is it even a pure perl issue I'm having? Cheers.

In reply to Fuse / Fuse::Simple write_buffer issues by jamescondron

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.