当 fanotify 打开时，多线程打开文件挂起
我使用这个 fanotify 示例来监视整个文件系统上的打开/访问权限(/)： http://git.infradead.org/users/eparis/fanotify-example.git。
然后我有一个具有多个线程的测试程序，每个线程迭代示例文件并打开/关闭其中的文件，有时我的程序挂在 open() 处。
操作系统：Ubuntu 2.6.38-11 x86_64。
不支持多线程开启是fanotify的bug吗？
我的测试程序的代码：
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <ctype.h>
#include <unistd.h>
#include <dirent.h>
#include <string.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <dirent.h>
//open file function
void open_file( char* file )
{
int fd = -1;
fd = open( file, O_WRONLY, 0x666 );
if( fd >= 0 )
{
printf("open:%s\n", file );
close( fd );
}
}
//iterate directory function
void printdir(char *dir, int depth)
{
DIR *dp;
struct stat statbuf;
char pathbuf[2048] = {0};
struct dirent entry;
struct dirent *entryPtr = NULL;
//printf("opendir %s\n", dir );
usleep( 300 );
if((dp = opendir(dir)) == NULL) {
if( errno != ENOTDIR )
{
fprintf(stderr,"cannot open directory: %s\n", dir);
perror("open fial");
}
return;
}
readdir_r( dp, &entry, &entryPtr );
while( entryPtr != NULL)
{
snprintf(pathbuf,2000, "%s/%s\0", dir, entry.d_name );
printf("iteraotr:%s\n", pathbuf );
lstat( pathbuf, &statbuf );
if(S_ISDIR( statbuf.st_mode ))
{
/* Found a directory, but ignore . and .. */
if(strcmp(".",entry.d_name) == 0 ||
strcmp("..",entry.d_name) == 0)
{
}
else
{
//printf("%d,%s\n",depth, entry->d_name);
printdir( pathbuf, depth+1);
}
}
else
{
//printf("%*s%s\n",depth,"",entry->d_name);
open_file( pathbuf );
}
readdir_r( dp, &entry, &entryPtr );
}
closedir(dp);
}
//thread function
void* iterator_dir( void* data )
{
char* path = (char*)data;
printf("In iterator_dir(): %s\n", path );
printdir( path, 0 );
return NULL;
}
pthread_t threadID[10] = {0};
//main function
int main( int argc, char** argv )
{
if( argc < 3 )
{
printf("Usage: %s <thread_num> <file>\n", argv[0] );
exit(0);
}
if( isdigit( (char)*argv[1] ) == 0 )
{
printf(" Thread num is 0 - 9\n");
exit(0);
}
int thread_num = atoi( argv[1] );
char* res;
pthread_attr_t attr;
pthread_attr_init(&attr);
int i = 0;
for( i = 0; i < thread_num; ++i )
{
pthread_create( &threadID[i], &attr, &iterator_dir, argv[2]);
}
for( i = 0; i < thread_num; ++i )
{
pthread_join( threadID[i] , &res );
}
}
2011-09-28 编辑：
我注释了打开文件操作，只保留迭代目录部分。该应用程序仍然挂起。 这是strace的输出：
enter code here
pid 10692] open("/home/byang//.config/menus", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC <unfinished ...>
[pid 10691] write(1, "1213966080 opendir /home/byang//"..., 56) = 56
……
[pid 10689] madvise(0x7f3c48dbc000, 8368128, MADV_DONTNEED) = 0
[pid 10689] _exit(0) = ?
Process 10689 detached
[pid 10688] <... futex resumed> ) = 0
[pid 10688] futex(0x7f3c47db99d0, FUTEX_WAIT, 10692, NULL <unfinished ...>
它挂在这里，当我关闭fanotify时，它继续……
[pid 10692] <... open resumed> ) = 11
[pid 10692] getdents(11, /* 4 entries */, 32768) = 128
[pid 10692] lstat("/home/byang//.config/menus/applications.menu", {st_mode=S_IFREG|0644, st_size=233, ...}) = 0
10688是父线程； 10689,10691,10692是迭代目录的子线程。 看来10692正在等待fanotify的回复？
I use this fanotify sample to monitor open/access perms on the whole file system(/): http://git.infradead.org/users/eparis/fanotify-example.git.
Then I have a test program with multiple threads, each thread iterate the sample foder and open/close the files in it, sometimes my program hangs at open().
OS: Ubuntu 2.6.38-11 x86_64.
Is it a bug of fanotify that it does not support multiple-thread opening?
The code of my test program:
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <ctype.h>
#include <unistd.h>
#include <dirent.h>
#include <string.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <dirent.h>
//open file function
void open_file( char* file )
{
int fd = -1;
fd = open( file, O_WRONLY, 0x666 );
if( fd >= 0 )
{
printf("open:%s\n", file );
close( fd );
}
}
//iterate directory function
void printdir(char *dir, int depth)
{
DIR *dp;
struct stat statbuf;
char pathbuf[2048] = {0};
struct dirent entry;
struct dirent *entryPtr = NULL;
//printf("opendir %s\n", dir );
usleep( 300 );
if((dp = opendir(dir)) == NULL) {
if( errno != ENOTDIR )
{
fprintf(stderr,"cannot open directory: %s\n", dir);
perror("open fial");
}
return;
}
readdir_r( dp, &entry, &entryPtr );
while( entryPtr != NULL)
{
snprintf(pathbuf,2000, "%s/%s\0", dir, entry.d_name );
printf("iteraotr:%s\n", pathbuf );
lstat( pathbuf, &statbuf );
if(S_ISDIR( statbuf.st_mode ))
{
/* Found a directory, but ignore . and .. */
if(strcmp(".",entry.d_name) == 0 ||
strcmp("..",entry.d_name) == 0)
{
}
else
{
//printf("%d,%s\n",depth, entry->d_name);
printdir( pathbuf, depth+1);
}
}
else
{
//printf("%*s%s\n",depth,"",entry->d_name);
open_file( pathbuf );
}
readdir_r( dp, &entry, &entryPtr );
}
closedir(dp);
}
//thread function
void* iterator_dir( void* data )
{
char* path = (char*)data;
printf("In iterator_dir(): %s\n", path );
printdir( path, 0 );
return NULL;
}
pthread_t threadID[10] = {0};
//main function
int main( int argc, char** argv )
{
if( argc < 3 )
{
printf("Usage: %s <thread_num> <file>\n", argv[0] );
exit(0);
}
if( isdigit( (char)*argv[1] ) == 0 )
{
printf(" Thread num is 0 - 9\n");
exit(0);
}
int thread_num = atoi( argv[1] );
char* res;
pthread_attr_t attr;
pthread_attr_init(&attr);
int i = 0;
for( i = 0; i < thread_num; ++i )
{
pthread_create( &threadID[i], &attr, &iterator_dir, argv[2]);
}
for( i = 0; i < thread_num; ++i )
{
pthread_join( threadID[i] , &res );
}
}
2011-09-28 Edit:
I comment the open file operation, only keep the iterate directory part. The application still hangs.
This is the output of strace:
enter code here
pid 10692] open("/home/byang//.config/menus", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC <unfinished ...>
[pid 10691] write(1, "1213966080 opendir /home/byang//"..., 56) = 56
.........
[pid 10689] madvise(0x7f3c48dbc000, 8368128, MADV_DONTNEED) = 0
[pid 10689] _exit(0) = ?
Process 10689 detached
[pid 10688] <... futex resumed> ) = 0
[pid 10688] futex(0x7f3c47db99d0, FUTEX_WAIT, 10692, NULL <unfinished ...>
It hangs here, when I close the fanotify, it continues...
[pid 10692] <... open resumed> ) = 11
[pid 10692] getdents(11, /* 4 entries */, 32768) = 128
[pid 10692] lstat("/home/byang//.config/menus/applications.menu", {st_mode=S_IFREG|0644, st_size=233, ...}) = 0
10688 is the parent thread; 10689,10691,10692 are the child threads that iterating the directories.
It seems that 10692 are waiting the reply from fanotify?
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评论（1）
这是内核 fanotify 的一个错误。
我发布了 Linux 内核的补丁：
当多个线程访问同一目录时，某些线程将挂起。
这个补丁让 fanotify 区分不同的访问事件
线程，防止 fanotify 合并来自不同线程的访问事件
线程。
http://marc.info/?l=linux-kernel&m =131822913806350&w=2
It's a bug of Kernel's fanotify.
I posted a patch to Linux-Kernel:
When multiple threadsiterate the same direcotry, some thread will hang.
This patch let fanotify differentiate access events from different
threads, prevent fanotify from merging access events from different
threads.
http://marc.info/?l=linux-kernel&m=131822913806350&w=2