El día martes, diciembre 22, 2020 a las 08:32:06p. m. +0100, Josef Wolf
escribió:
> On Tue, Dec 22, 2020 at 04:58:53PM +0100, Matthias Apitz wrote:
> > And what is this repeated asking with lseek(2) from line 22 to 89 in
> > both cases with
> >
> > 22617 lseek(4, 0, SEEK_CUR) = 4096
> >
> > always getting "yes, next byte to read is number 4096" I don't know where
> > maildir files in mutt are handled.
>
> As I wrote in my prevous post, this are 68 invocations to lseek() and the mail
> file contains 68 header lines. I guess those lseek() calls are somewhere deep
> inside fgets() which mutt uses to read the header line-by-line.
>
> ...
Why fgets(3) should do that? The first fgets(3) call will use a read(2)
sys call to read (as shown in your strace's output) 4096 bytes and every
fgets(3) call will return the bytes until a '\n'; and then the next
line from its internal buffer, until this is exhausted.
I wrote a small C pgm as:
#include <stdio.h>
int main()
{
FILE *fp;
char str[4097];
fp = fopen("mail", "r");
while( fgets(str, 4096, fp) != NULL ) {
printf("%s", str);
}
fclose(fp);
return(0);
}
and if you run this with "truss -o tr ./a.out" (FreeBSD has currently no
strace(1)), you will see exactly this:
...
open("mail",O_RDONLY,0666) = 3 (0x3)
fstat(3,{ mode=-rw------- ,inode=13942391,size=4539,blksize=32768 }) = 0 (0x0)
read(3,"From mutt-users-boun...@mutt.org"...,32768) = 4539 (0x11bb)
fstat(1,{ mode=crw--w---- ,inode=402,size=0,blksize=4096 }) = 0 (0x0)
ioctl(1,TIOCGETA,0x7fffffffced0) = 0 (0x0)
write(1,"From mutt-users-boun...@mutt.org"...,58) = 58 (0x3a)
write(1,"Return-Path: <mutt-users-bounces"...,43) = 43 (0x2b)
write(1,"Delivered-To: w51246_0-guru@mb-1"...,42) = 42 (0x2a)
...
write(1,"j...@raven.inka.de\n",17) = 17 (0x11)
write(1,"\n",1) = 1 (0x1)
read(3,0x800a09180,32768) = 0 (0x0)
close(3) = 0 (0x0)
exit(0x0)
i.e. no further lseek(2) sys calls.
matthias
--
Matthias Apitz, ✉ g...@unixarea.de, http://www.unixarea.de/ +49-176-38902045
Public GnuPG key: http://www.unixarea.de/key.pub
Без книги нет знания, без знания нет коммунизма (Влaдимир Ильич Ленин)
Without books no knowledge - without knowledge no communism (Vladimir Ilyich
Lenin)
Sin libros no hay saber - sin saber no hay comunismo. (Vladimir Ilich Lenin)
