CONFIG_NFS_DIRECTIO: Allow direct I/O on NFS files

General informations

The Linux kernel configuration item CONFIG_NFS_DIRECTIO has multiple definitions:

Allow direct I/O on NFS files found in fs/Kconfig

The configuration item CONFIG_NFS_DIRECTIO:

• prompt: Allow direct I/O on NFS files
• type: bool
• depends on: CONFIG_NFS_FS
• defined in fs/Kconfig
• found in Linux kernels: 2.6.19–2.6.25

Help text

This option enables applications to perform uncached I/O on files in NFS file systems using the O_DIRECT open() flag. When O_DIRECT is set for a file, its data is not cached in the system's page cache. Data is moved to and from user-level application buffers directly. Unlike local disk-based file systems, NFS O_DIRECT has no alignment restrictions.

Unless your program is designed to use O_DIRECT properly, you are much better off allowing the NFS client to manage data caching for you. Misusing O_DIRECT can cause poor server performance or network storms. This kernel build option defaults OFF to avoid exposing system administrators unwittingly to a potentially hazardous feature.

For more details on NFS O_DIRECT, see fs/nfs/direct.c.

If unsure, say N. This reduces the size of the NFS client, and causes open() to return EINVAL if a file residing in NFS is opened with the O_DIRECT flag.

Allow direct I/O on NFS files (EXPERIMENTAL) found in fs/Kconfig

The configuration item CONFIG_NFS_DIRECTIO:

• prompt: Allow direct I/O on NFS files (EXPERIMENTAL)
• type: bool
• depends on: CONFIG_NFS_FS && CONFIG_EXPERIMENTAL
• defined in fs/Kconfig
• found in Linux kernels: 2.6.0–2.6.18

Help text

This option enables applications to perform uncached I/O on files in NFS file systems using the O_DIRECT open() flag. When O_DIRECT is set for a file, its data is not cached in the system's page cache. Data is moved to and from user-level application buffers directly. Unlike local disk-based file systems, NFS O_DIRECT has no alignment restrictions.

Unless your program is designed to use O_DIRECT properly, you are much better off allowing the NFS client to manage data caching for you. Misusing O_DIRECT can cause poor server performance or network storms. This kernel build option defaults OFF to avoid exposing system administrators unwittingly to a potentially hazardous feature.

For more details on NFS O_DIRECT, see fs/nfs/direct.c.

If unsure, say N. This reduces the size of the NFS client, and causes open() to return EINVAL if a file residing in NFS is opened with the O_DIRECT flag.

Hardware

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The data is retrived from:

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• Linux Kernel Driver DataBase (LKDDb)

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