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Oh no mkstemp is already obsolete (in Linux), now we have O_TMPFILE [1] for creating temporary files that do not even have names... [1] https://lwn.net/Article

Oh no mkstemp is already obsolete (in Linux), now we have O_TMPFILE [1] for creating temporary files that do not even have names... [1] https://lwn.net/Articles/557314/ https://lwn.net/Articles/557314/

masklinn 13y ago
I don't think that makes mkstemp obsolete as it may be important to have named temp files. (and of course though there is a slight race you can unlink the file you get through mkstemp while keeping it open, that seems to be the strategy used by python's tempfile.TemporaryFile)
- justincormack 13y ago
  I can't think of any case, except if you are too lazy to pass a file descriptor to another process, and its easier to pass the name (which cannot be ruled out, it is easier!). You can't safely close and reopen the file, or it might have been modified. There is still a possibility that an attacker opens the file before you unlink it and starts writing to it, which O_TMPFILE gets rid of as it never has a name so can never be opened.
  - qu4z-2 13y ago
    Does every program which accepts filenames also accept file descriptors? I can definitely see the use of having a name to pass around.
    - nisse72 13y ago
      On Linux at least (not sure about OpenBSD), every open file has a name somewhere in /proc, so you could pass that.
      - masklinn 13y ago
        Which defeats having a flag for an "invisible" temp file, since it'll still be visible (and accessible) in /proc.
  - caf 13y ago
    The case where a name is required is where you want to rename or link the temporary file to a new, permanent name in the filesystem.
  - skybrian 13y ago
    It's also useful for debugging. If the file has a name, you can look at the file while the program is stopped in a debugger.
  - mortehu 13y ago
    How about whenever you're writing a non=temporary file? I do this all the time: 1. Create temporary file in the same directory as the target path. 2. Write and fsync the temporary file 3. Rename the temporary file to the target filename Oh, and on Linux you can open even deleted files by using /proc/<N>/fd/<M>. It may look like a symlink, but it's not.
    - justincormack 13y ago
      OK that's a good reason!
    - justincormack 13y ago
      You can create files form the fd you get from O_TMPFILE it turns out http://lwn.net/SubscriberLink/562488/3c6d56bef275c0b4/ http://lwn.net/SubscriberLink/562488/3c6d56bef275c0b4/
asveikau 13y ago
Even ignoring the fact that these are not exactly the same... How does introducing a new interface necessarily "obsolete" the old one? Particularly when the old one is part of a standard, and the new one is not.

masklinn 13y ago

I don't think that makes mkstemp obsolete as it may be important to have named temp files. (and of course though there is a slight race you can unlink the file you get through mkstemp while keeping it open, that seems to be the strategy used by python's tempfile.TemporaryFile)

justincormack 13y ago
I can't think of any case, except if you are too lazy to pass a file descriptor to another process, and its easier to pass the name (which cannot be ruled out, it is easier!). You can't safely close and reopen the file, or it might have been modified. There is still a possibility that an attacker opens the file before you unlink it and starts writing to it, which O_TMPFILE gets rid of as it never has a name so can never be opened.
- qu4z-2 13y ago
  Does every program which accepts filenames also accept file descriptors? I can definitely see the use of having a name to pass around.
  - nisse72 13y ago
    On Linux at least (not sure about OpenBSD), every open file has a name somewhere in /proc, so you could pass that.
    - masklinn 13y ago
      Which defeats having a flag for an "invisible" temp file, since it'll still be visible (and accessible) in /proc.
- caf 13y ago
  The case where a name is required is where you want to rename or link the temporary file to a new, permanent name in the filesystem.
- skybrian 13y ago
  It's also useful for debugging. If the file has a name, you can look at the file while the program is stopped in a debugger.
- mortehu 13y ago
  How about whenever you're writing a non=temporary file? I do this all the time: 1. Create temporary file in the same directory as the target path. 2. Write and fsync the temporary file 3. Rename the temporary file to the target filename Oh, and on Linux you can open even deleted files by using /proc/<N>/fd/<M>. It may look like a symlink, but it's not.
  - justincormack 13y ago
    OK that's a good reason!
  - justincormack 13y ago
    You can create files form the fd you get from O_TMPFILE it turns out http://lwn.net/SubscriberLink/562488/3c6d56bef275c0b4/ http://lwn.net/SubscriberLink/562488/3c6d56bef275c0b4/

asveikau 13y ago

Even ignoring the fact that these are not exactly the same... How does introducing a new interface necessarily "obsolete" the old one? Particularly when the old one is part of a standard, and the new one is not.