Messages in this thread | | | Date | Wed, 10 Apr 2002 19:08:27 +0200 | From | "E. Abbink" <> | Subject | Problem using mandatory locks (other apps can read/delete etc) |
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Hi,
I'm trying to solve a problem using mandatory locks but am having some difficulty in doing so. (if there's a more appropriate place for discussing this please ignore the rest of this post. pointers to that place would be appreciated ;) )
my problem:
when I lock a file with a mandatory write lock (ie. fcntl, +s-x bits and mand mount option. for code see below) it is still possible:
- for me to rm the file in question - for the file to be read by an other process
It's not possible to cat to the file or cp another file over it (as expected). For my application I want a locked file to be completely locked/protected from other processes.
If I retry the same without setting the +s-x bits the cp & cat succeed, so something special is being done in the first case.
According to all docs (i can find) mandatory locks should block both the read and write system calls (i cant find anything in it regarding unlink though...). In my case however it seems as if only write calls are blocked but not read calls?
If anyone could shed any light on this it would be much appreciated.
Esger
system details:
linux 2.4.17 partially suse & xfs patched kernel filesystem is reiserfs i386 dual pIII450
test app code:
int main () { int fd ;
fd = open ("image.jpg", O_RDWR) ;
if (fd == -1) { printf ("error %d while opening file\n", errno) ; exit (1) ; }
struct flock lock ;
lock.l_type = F_WRLCK ; lock.l_whence = SEEK_SET ; lock.l_start = 0 ; lock.l_len = 0 ; lock.l_pid = 0 ; // ignored
int err = fcntl (fd, F_SETLK, &lock) ;
if (err == -1) { printf ("error %d while locking file\n", errno) ; exit (1) ; } else printf ("file locked\n") ;
while (1) sleep (1) ; }
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