Is it safe to close a directory stream (DIR *) in both the parent and child process?
This page describes the guaranteed behavior of the functions readdir and readdir_r and contains the following sentence:
After a call to fork(), either the parent or child (but not both) may
continue processing the directory stream using readdir(), rewinddir()
or seekdir(). If both the parent and child processes use these
functions, the result is undefined.
I'm writing a fork-safe wrapper around the DIR*-related family of functions as an exercise and I'm wondering whether it's safe to closedir the directory stream in both the parent and the child simultaneously or whether the process that doesn't continue reading from the directory stream isn't supposed to interact with the directory stream at all.
posix
asked 6 hours ago
Gregory NisbetGregory Nisbet
1,4691020
add a comment |
This page describes the guaranteed behavior of the functions readdir and readdir_r and contains the following sentence:
After a call to fork(), either the parent or child (but not both) may
continue processing the directory stream using readdir(), rewinddir()
or seekdir(). If both the parent and child processes use these
functions, the result is undefined.
I'm writing a fork-safe wrapper around the DIR*-related family of functions as an exercise and I'm wondering whether it's safe to closedir the directory stream in both the parent and the child simultaneously or whether the process that doesn't continue reading from the directory stream isn't supposed to interact with the directory stream at all.
posix
asked 6 hours ago
Gregory NisbetGregory Nisbet
1,4691020
1
Executing in other process needs ptrace. Or you have setup IPC between parent and child so they can communicate and do the requested action.
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I was going to have a static atomic flag and register aforkhandler and force the user to pick whenopendiring the directory whether the parent or child inherits it on fork. My wrapper library that doesn't exist yet will promise nothing if you use the unwrapped library calls in addition to the wrapper.
– Gregory Nisbet
3 hours ago
Don't know what you're talking about. If you want disallow some process from accessing some file, then use mount namespace or simply revoke the file permissions for that user or use selinux or whatever. Then that process can only get an fd from another privileged process
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I see. I'm not trying to force processes that I have no control over to "play by the POSIX rules" or prevent them for accessing particular files. I'm trying to understand what exactly the POSIX rules are regarding directory streams. My motivation for understanding what the rules are is to write a wrapper library around the POSIX API that makes it easier to write programs that only use the API in defined ways.
– Gregory Nisbet
3 hours ago
add a comment |
This page describes the guaranteed behavior of the functions readdir and readdir_r and contains the following sentence:
After a call to fork(), either the parent or child (but not both) may
continue processing the directory stream using readdir(), rewinddir()
or seekdir(). If both the parent and child processes use these
functions, the result is undefined.
I'm writing a fork-safe wrapper around the DIR*-related family of functions as an exercise and I'm wondering whether it's safe to closedir the directory stream in both the parent and the child simultaneously or whether the process that doesn't continue reading from the directory stream isn't supposed to interact with the directory stream at all.
posix
asked 6 hours ago
Gregory NisbetGregory Nisbet
1,4691020
This page describes the guaranteed behavior of the functions readdir and readdir_r and contains the following sentence:
After a call to fork(), either the parent or child (but not both) may
continue processing the directory stream using readdir(), rewinddir()
or seekdir(). If both the parent and child processes use these
functions, the result is undefined.
I'm writing a fork-safe wrapper around the DIR*-related family of functions as an exercise and I'm wondering whether it's safe to closedir the directory stream in both the parent and the child simultaneously or whether the process that doesn't continue reading from the directory stream isn't supposed to interact with the directory stream at all.
posix
posix
asked 6 hours ago
Gregory NisbetGregory Nisbet
1,4691020
asked 6 hours ago
Gregory NisbetGregory Nisbet
1,4691020
asked 6 hours ago
Gregory NisbetGregory Nisbet
1,4691020
asked 6 hours ago
Gregory NisbetGregory Nisbet
1,4691020
asked 6 hours ago
Gregory NisbetGregory Nisbet
1,4691020
1,4691020
1
Executing in other process needs ptrace. Or you have setup IPC between parent and child so they can communicate and do the requested action.
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I was going to have a static atomic flag and register aforkhandler and force the user to pick whenopendiring the directory whether the parent or child inherits it on fork. My wrapper library that doesn't exist yet will promise nothing if you use the unwrapped library calls in addition to the wrapper.
– Gregory Nisbet
3 hours ago
Don't know what you're talking about. If you want disallow some process from accessing some file, then use mount namespace or simply revoke the file permissions for that user or use selinux or whatever. Then that process can only get an fd from another privileged process
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I see. I'm not trying to force processes that I have no control over to "play by the POSIX rules" or prevent them for accessing particular files. I'm trying to understand what exactly the POSIX rules are regarding directory streams. My motivation for understanding what the rules are is to write a wrapper library around the POSIX API that makes it easier to write programs that only use the API in defined ways.
– Gregory Nisbet
3 hours ago
add a comment |
1
Executing in other process needs ptrace. Or you have setup IPC between parent and child so they can communicate and do the requested action.
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I was going to have a static atomic flag and register aforkhandler and force the user to pick whenopendiring the directory whether the parent or child inherits it on fork. My wrapper library that doesn't exist yet will promise nothing if you use the unwrapped library calls in addition to the wrapper.
– Gregory Nisbet
3 hours ago
Don't know what you're talking about. If you want disallow some process from accessing some file, then use mount namespace or simply revoke the file permissions for that user or use selinux or whatever. Then that process can only get an fd from another privileged process
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I see. I'm not trying to force processes that I have no control over to "play by the POSIX rules" or prevent them for accessing particular files. I'm trying to understand what exactly the POSIX rules are regarding directory streams. My motivation for understanding what the rules are is to write a wrapper library around the POSIX API that makes it easier to write programs that only use the API in defined ways.
– Gregory Nisbet
3 hours ago
1
1
Executing in other process needs ptrace. Or you have setup IPC between parent and child so they can communicate and do the requested action.
– 炸鱼薯条德里克
3 hours ago
Executing in other process needs ptrace. Or you have setup IPC between parent and child so they can communicate and do the requested action.
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I was going to have a static atomic flag and register a
fork handler and force the user to pick when opendiring the directory whether the parent or child inherits it on fork. My wrapper library that doesn't exist yet will promise nothing if you use the unwrapped library calls in addition to the wrapper.– Gregory Nisbet
3 hours ago
@炸鱼薯条德里克 I was going to have a static atomic flag and register a
fork handler and force the user to pick when opendiring the directory whether the parent or child inherits it on fork. My wrapper library that doesn't exist yet will promise nothing if you use the unwrapped library calls in addition to the wrapper.– Gregory Nisbet
3 hours ago
Don't know what you're talking about. If you want disallow some process from accessing some file, then use mount namespace or simply revoke the file permissions for that user or use selinux or whatever. Then that process can only get an fd from another privileged process
– 炸鱼薯条德里克
3 hours ago
Don't know what you're talking about. If you want disallow some process from accessing some file, then use mount namespace or simply revoke the file permissions for that user or use selinux or whatever. Then that process can only get an fd from another privileged process
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I see. I'm not trying to force processes that I have no control over to "play by the POSIX rules" or prevent them for accessing particular files. I'm trying to understand what exactly the POSIX rules are regarding directory streams. My motivation for understanding what the rules are is to write a wrapper library around the POSIX API that makes it easier to write programs that only use the API in defined ways.
– Gregory Nisbet
3 hours ago
@炸鱼薯条德里克 I see. I'm not trying to force processes that I have no control over to "play by the POSIX rules" or prevent them for accessing particular files. I'm trying to understand what exactly the POSIX rules are regarding directory streams. My motivation for understanding what the rules are is to write a wrapper library around the POSIX API that makes it easier to write programs that only use the API in defined ways.
– Gregory Nisbet
3 hours ago
add a comment |
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Executing in other process needs ptrace. Or you have setup IPC between parent and child so they can communicate and do the requested action.
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I was going to have a static atomic flag and register a
forkhandler and force the user to pick whenopendiring the directory whether the parent or child inherits it on fork. My wrapper library that doesn't exist yet will promise nothing if you use the unwrapped library calls in addition to the wrapper.– Gregory Nisbet
3 hours ago
Don't know what you're talking about. If you want disallow some process from accessing some file, then use mount namespace or simply revoke the file permissions for that user or use selinux or whatever. Then that process can only get an fd from another privileged process
– 炸鱼薯条德里克
3 hours ago
@炸鱼薯条德里克 I see. I'm not trying to force processes that I have no control over to "play by the POSIX rules" or prevent them for accessing particular files. I'm trying to understand what exactly the POSIX rules are regarding directory streams. My motivation for understanding what the rules are is to write a wrapper library around the POSIX API that makes it easier to write programs that only use the API in defined ways.
– Gregory Nisbet
3 hours ago