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(struct map_iterator): Add members "buf_size", "buf", and "buf_end".

Browse source 
(maps_init): Try to mmap() a one-page buffer and, if successful,
	initialize the new map_iterator members based on it.
(maps_next): If the one-page buffer is available, use it to read
	/proc/PID/maps.  This avoids expensive lseek() calls which,
	in the case of /proc lead to T(n) = O(n^2) behavior.

(Logical change 1.208)
This commit is contained in:
mostang.com!davidm 2004-04-21 03:56:06 +00:00
parent 6840f3c057
commit 5de4b351e7
1 changed files with 72 additions and 14 deletions
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86
src/os-linux.h
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@ -30,6 +30,9 @@ struct map_iterator
{
off_t offset;
int fd;
size_t buf_size;
char *buf;
char *buf_end;
};
static inline char *
@ -68,6 +71,15 @@ maps_init (struct map_iterator *mi, pid_t pid)
mi->fd = open (path, O_RDONLY);
mi->offset = 0;
/* Try to allocate a page-sized buffer. If that fails, we'll fall
back on reading one line at a time. */
mi->buf_size = getpagesize ();
cp = mmap (0, mi->buf_size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (cp == MAP_FAILED)
cp = NULL;
mi->buf = mi->buf_end = cp;
}
static inline char *
@ -182,28 +194,74 @@ maps_next (struct map_iterator *mi,
while (1)
{
lseek (mi->fd, mi->offset, SEEK_SET);
if ((nread = read (mi->fd, line, to_read)) <= 0)
return 0;
for (i = 0; i < nread && line[i] != '\n'; ++i)
/* skip */;
if (i < nread)
if (mi->buf)
{
line[i] = '\0';
mi->offset += i + 1;
ssize_t bytes_left = mi->buf_end - mi->buf;
char *eol = NULL;
for (i = 0; i < bytes_left; ++i)
{
if (mi->buf[i] == '\n')
{
eol = mi->buf + i;
break;
}
else if (mi->buf[i] == '\0')
break;
}
if (!eol)
{
/* copy down the remaining bytes, if any */
if (bytes_left > 0)
memcpy (mi->buf_end - mi->buf_size, mi->buf, bytes_left);
mi->buf = mi->buf_end - mi->buf_size;
nread = read (mi->fd, mi->buf + bytes_left,
mi->buf_size - bytes_left);
if (nread <= 0)
return 0;
eol = mi->buf + bytes_left + nread - 1;
for (i = bytes_left; i < bytes_left + nread; ++i)
if (mi->buf[i] == '\n')
{
eol = mi->buf + i;
break;
}
}
cp = mi->buf;
mi->buf = eol + 1;
*eol = '\0';
}
else
{
if (to_read < sizeof (line))
to_read = sizeof (line) - 1;
/* maps_init() wasn't able to allocate a buffer; do it the
slow way. */
lseek (mi->fd, mi->offset, SEEK_SET);
if ((nread = read (mi->fd, line, to_read)) <= 0)
return 0;
for (i = 0; i < nread && line[i] != '\n'; ++i)
/* skip */;
if (i < nread)
{
line[i] = '\0';
mi->offset += i + 1;
}
else
mi->offset += nread; /* not supposed to happen... */
continue; /* duh, no newline found */
{
if (to_read < sizeof (line))
to_read = sizeof (line) - 1;
else
mi->offset += nread; /* not supposed to happen... */
continue; /* duh, no newline found */
}
cp = line;
}
/* scan: "LOW-HIGH PERM OFFSET MAJOR:MINOR INUM PATH" */
cp = scan_hex (line, low);
cp = scan_hex (cp, low);
cp = scan_char (cp, &dash);
cp = scan_hex (cp, high);
cp = scan_string (cp, perm, sizeof (perm));