please find the inlined comments.
Hello,
I’m trying to store additional metadata like content-type and etc at extended attribute.
My client code are like
fd = glusterfs_open( path );
glusterfs_write( fd, data, data_length );
glusterfs_close( fd ); //------
glusterfs_setxattr( path, attr_name, attr_value, value_length,0 );
My concern is that above client code runs on multiple machines and multi-threaded.
In higher concurrency, client A could write content, client B write content, client B write its attribute then client A write its attribute.
So to speak, file content comes from client B but attribute comes from client A.
If I use a lock server, I can guarantee data integrity. But is there a simpler way to store extended attributes at an atomic environment?
locks should be used to ensure atomicity. There is no other simpler way which I can think of.
I see another function, glusterfs_fsetxattr which accepts open glusterfs_file descriptor. If I rewrite as following, can I guarantee the integrity?
fd = glusterfs_open( path );
glusterfs_write( fd, data, data_length );
glusterfs_fsetxattr( fd, attr_name, attr_value, value_length,0 );
glusterfs_close( fd );
No.
One of the solutions I can think of is,
fd = glusterfs_open( path );
glusterfs_fcntl (fd, F_SETLKW, flock); /* flock tries to hold write lock on whole file */
/* please note usage of F_SETLKW, If you want to use F_SETLK you have to check for */
/* return value and proceed with writing only after lock has been acquired */
glusterfs_write( fd, data, data_length );
glusterfs_setxattr( path, attr_name, attr_value, value_length,0 );
glusterfs_fcntl (fd, F_SETLKW, flock); /*flock tries to unlock */
glusterfs_close( fd ); //------
Thanks
DongMin Yu
HOSTWAY IDC Corp. / R&D Principal Researcher
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regards,
--
Raghavendra G
