Operating System Transactions
Operating System Transactions Donald E. Porter, Owen S. Hofmann, Christopher J. Rossbach, Alexander Benn, and Emmett Witchel Department of Computer Sciences, The University of Texas at Austin {porterde,osh,rossbach,abenn1,witchel}@cs.utexas.edu ABSTRACT Programming; D.4.7 [Operating Systems]: Organization Applications must be able to synchronize accesses to oper- and Design ating system resources in order to ensure correctness in the face of concurrency and system failures. System transac- General Terms tions allow the programmer to specify updates to heteroge- Design, Performance, Security neous system resources with the OS guaranteeing atomicity, consistency, isolation, and durability (ACID). System trans- Keywords actions efficiently and cleanly solve persistent concurrency Transactions, Operating Systems, TxOS, Race Conditions, problems that are difficult to address with other techniques. Transactional Memory For example, system transactions eliminate security vulner- abilities in the file system that are caused by time-of-check- 1. INTRODUCTION to-time-of-use (TOCTTOU) race conditions. System trans- actions enable an unsuccessful software installation to roll Applications often need to group accesses to operating system resources (such as files and signals) into logical units, back without disturbing concurrent, independent updates to the file system. just as multithreaded applications must group accesses to This paper describes TxOS, a variant of Linux 2.6.22 that shared data structures into critical regions. For example, implements system transactions. TxOS uses new implemen- local user and group accounts on Linux and similar oper- tation techniques to provide fast, serializable transactions ating systems are stored across three files that need to be /etc/passwd /etc/shadow with strong isolation and fairness between system transac- mutually consistent: , , and /etc/group.
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