Veritas™ File System Programmer's Reference Guide - Solaris

Last Published:
Product(s): InfoScale & Storage Foundation (7.2)
Platform: Solaris
  1. Veritas File System software developer's kit
    1.  
      About the software developer's kit
    2. File System software developer's kit features
      1.  
        API library interfaces
      2.  
        File Change Log
      3.  
        Multi-volume support
      4.  
        Veritas File System I/O
    3.  
      Software developer's kit packages
    4.  
      Required libraries and header files
    5. Compiling environment
      1.  
        Recompiling with a different compiler
  2. File Change Log
    1. About the File Change Log file
      1.  
        Recorded changes
      2. Using the File Change Log file
        1.  
          Space usage
        2.  
          Full system scan reductions
        3.  
          File history traces
      3.  
        File Change Log logging activation
      4. File Change Log file layout
        1.  
          File Change Log superblock
        2.  
          File Change Log record
    2. Record types
      1.  
        Special records
      2.  
        Typical record sequences
    3. File Change Log tunables
      1.  
        How tunables handle File Change Log growth size
    4. Application programming interface for File Change Log
      1.  
        Ease of use
      2.  
        Backward compatibility
      3. API functions
        1.  
          Functions for accessing File Change Log records
        2.  
          Functions for seeking offsets and time stamps in the File Change Log
        3. vxfs_fcl_open
          1.  
            Return value
        4. vxfs_fcl_close
          1.  
            Parameters
        5. vxfs_fcl_getinfo
          1.  
            Return values
        6. vxfs_fcl_read
          1.  
            Parameters
          2.  
            Input
          3.  
            Output
          4.  
            Return values
        7. vxfs_fcl_getcookie
          1.  
            Parameters
        8. vxfs_fcl_seek
          1.  
            Parameters
          2.  
            Return values
        9. vxfs_fcl_seektime
          1.  
            Parameters
          2.  
            Return values
        10. vxfs_fcl_sync
          1.  
            Parameters
      4. File Change Log record
        1.  
          Defines
        2.  
          fcl_iostats structure
        3.  
          fcl_acsinfo structure
        4.  
          Record structure fields
      5. Copying File Change Log records
        1.  
          Index maintenance application
        2. Computing a usage profile
          1.  
            Initial setup
          2.  
            Sample steps
          3.  
            Off host processing
      6. Veritas File System and File Change Log upgrade and downgrade
        1.  
          Converting File Change Log version 3 files to version 4
        2.  
          Downgrading Veritas File System versions
    5. Reverse path name lookup
      1.  
        Inodes
      2.  
        vxfs_inotopath_gen
  3. Multi-volume support
    1.  
      About multi-volume support
    2.  
      Uses for multi-volume support
    3. Volume application programming interfaces
      1.  
        Administering volume sets
      2.  
        Querying the volume set for a file system
      3.  
        Modifying a volume within a file system
      4.  
        Encapsulationg and de-encapsulating a volume
    4. Allocation policy application programming interfaces
      1.  
        Directing file allocations
      2.  
        Creating and assigning policies
      3.  
        Querying the defined policies
      4.  
        Enforcing a policy
    5.  
      Data structures
    6. Using policies and application programming interfaces
      1.  
        Defining and assigning allocation policies
      2.  
        Using volume application programming interfaces
  4. Named data streams
    1.  
      About named data streams
    2.  
      Uses for named data streams
    3.  
      Named data streams application programming interface
    4.  
      Listing named data streams
    5.  
      Namespace for named data streams
    6.  
      Behavior changes in other system calls
    7.  
      Querying named data streams
    8.  
      Application programming interface
    9.  
      Command reference
  5. Veritas File System I/O
    1.  
      About Veritas File System I/O
    2.  
      Freeze and thaw
    3. Caching advisories
      1.  
        Direct I/O
      2.  
        Concurrent I/O
      3.  
        Unbuffered I/O
      4.  
        Other advisories
    4. Extents
      1. Extent attributes
        1.  
          Attribute specifics
      2.  
        Reservation: preallocating space to a file
      3.  
        Fixed extent size
      4.  
        Application programming interface for extent attributes
      5. Allocation flags
        1.  
          Allocation flags with reservation
        2.  
          Reservation trimming
        3.  
          Non-persistent reservation
        4.  
          No write beyond reservation
        5.  
          Contiguous reservation
        6.  
          Include reservation in the file size
        7.  
          Reading the grown part of the file
      6.  
        Allocation flags with fixed extent size
      7.  
        How to use extent attribute APIs
      8.  
        Setting fixed extent size
  6. Thin Reclamation
    1.  
      About Thin Storage
    2.  
      About Thin Reclamation
    3. Thin Reclamation application programming interface
      1.  
        vxfs_ts_reclaim return values

Concurrent I/O

Concurrent I/O (VX_CONCURRENT) is a form of I/O for file access. This form of I/O allows multiple processes to read or write to the same file without blocking other read() or write() operations. POSIX semantics requires read() and write() operations to be serialized on a file with other read() and write() operations. With POSIX semantics, a read will either read the data before or after the write occurs. With the VX_CONCURRENT advisory set on a file, the reads and writes are not serialized similar to character devices. Applications that require high performance for accessing data and do not perform overlapping writes to the same file generally use this advisory. An example is database applications. Such applications perform their own locking at the application level to avoid overlapping writes to the same region of the file.

It is the responsibility of the application or threads to coordinate write activities to the same file when using the VX_CONCURRENT advisory to avoid overlapping writes. The consequence of two overlapping writes to the same file is unpredictable. The best practice for applications is to avoid simultaneous write operations to the same region of the same file.

If the VX_CONCURRENT advisory is set on a file, VxFS performs direct I/O for reads and writes to the file. As such, concurrent I/O has the same alignment requirements as direct I/O.

See Direct I/O.

When concurrent I/O is enabled, the read and write behaves as follows:

  • The write() system call acquires a shared read-write lock instead of an exclusive lock.

  • The write() system call performs direct I/O to the disk instead of copying and then writing the user data to the pages in the system page cache.

  • The read() system call acquires a shared read-write lock and performs direct I/O from disk instead of reading the data into pages in the system page cache and copying from the pages to the user buffer.

  • The read() and write() system calls are not atomic. The application must ensure that two threads do not write to the same region of a file at the same time.

Concurrent I/O (CIO) can be set through the file descriptor and ioctl() operation using the VX_SETCACHE ioctl command with the VX_CONCURRENT advisory flag. Only the read() and write() operations occurring through this file descriptor use concurrent I/O. read() and write() operations occurring through other file descriptors still follows the POSIX semantics. The VX_CONCURRENT advisory can be set by the VX_SETCACHE ioctl descriptor on a file.

CIO is a licensable feature of VxFS.