Messages in this thread | | | From | Andy Lutomirski <> | Date | Sat, 30 Mar 2013 15:40:55 -0700 | Subject | Re: New copyfile system call - discuss before LSF? |
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On Sat, Mar 30, 2013 at 12:49 PM, Pavel Machek <pavel@ucw.cz> wrote: > Hi! > >> > I thought the first thing people would ask for is to atomically create a >> > new file and copy the old file into it (at least on local file systems). >> > The idea is that nothing should see an empty destination file, either >> > by race or by crash. (This feature would perhaps be described as a >> > pony, but it should be implementable.) >> >> Having already wasted many week trying to implement your pony, I would >> consider it about as possible as winning the lottery three times in a >> row. It clearly is in theory and yet,... > > Hmm, really? AFAICT it would be simple to provide open_deleted_file("directory") > syscall. You'd open_deleted_file(), copy source file into it, then > fsync(), then link it into filesystem.
Isn't linking a deleted file back into the filesystem explicitly forbidden? I'm pretty sure that linking from /proc/fd/whatever doesn't work. (I've often wanted a flink system call that takes a file descriptor and links it somewhere. If it came with an option to control whether it would overwrite an existing file, even better.)
--Andy
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