class VmoFile

Defined at line 24 of file ../../sdk/lib/vfs/cpp/vmo_file.h

A file node backed by a range of bytes in a VMO.

The file has a fixed size specified at creating time; it does not grow or shrink even when

written into.

This class is thread-safe.

Public Methods

void VmoFile (zx::vmo vmo, size_t length, WriteMode write_option, DefaultSharingMode vmo_sharing)

Creates a file node backed by a VMO.

Defined at line 65 of file ../../sdk/lib/vfs/cpp/vmo_file.h

zx_status_t Serve (fuchsia_io::Flags flags, fidl::ServerEnd<fuchsia_io::File> server_end, async_dispatcher_t * dispatcher)

Serve a new connection to this VMO-file on `server_end` using specified `flags`.

This method must only be used with a single-threaded asynchronous dispatcher. If `dispatcher`

is `nullptr`, the current thread's default dispatcher will be used via

`async_get_default_dispatcher`. The same `dispatcher` must be used if multiple connections are

served for the same node, otherwise `ZX_ERR_INVALID_ARGS` will be returned.

Defined at line 75 of file ../../sdk/lib/vfs/cpp/vmo_file.h

zx::unowned_vmo vmo ()

Returns a borrowed handle to the VMO backing this file.

Defined at line 85 of file ../../sdk/lib/vfs/cpp/vmo_file.h

Enumerations

enum class WriteMode : vfs_internal_write_mode_t

Name	Value	Comments
kReadOnly	VFS_INTERNAL_WRITE_MODE_READ_ONLY	The VmoFile is read only.
kWritable	VFS_INTERNAL_WRITE_MODE_WRITABLE	The VmoFile will be writable.

Specifies the desired behavior of writes.

Defined at line 27 of file ../../sdk/lib/vfs/cpp/vmo_file.h

enum class DefaultSharingMode : vfs_internal_sharing_mode_t

Name	Value	Comments
kNone	VFS_INTERNAL_SHARING_MODE_NONE	Will return `ZX_ERR_NOT_SUPPORTED` if a sharing mode was not specified in the request.
kDuplicate	VFS_INTERNAL_SHARING_MODE_DUPLICATE	The VMO handle is duplicated for each client. This is appropriate when it is okay for clients to access the entire contents of the VMO, possibly extending beyond the pages spanned by the file. This mode is significantly more efficient than \|CLONE_COW\| and should be preferred when file spans the whole VMO or when the VMO's entire content is safe for clients to read.
kCloneCow	VFS_INTERNAL_SHARING_MODE_COW	The VMO range spanned by the file is cloned on demand, using copy-on-write semantics to isolate modifications of clients which open the file in a writable mode. This is appropriate when clients need to be restricted from accessing portions of the VMO outside of the range of the file and when file modifications by clients should not be visible to each other.

Name

Value

Comments

kNone

VFS_INTERNAL_SHARING_MODE_NONE

Will return `ZX_ERR_NOT_SUPPORTED` if a sharing mode was not specified in the request.

kDuplicate

VFS_INTERNAL_SHARING_MODE_DUPLICATE

The VMO handle is duplicated for each client.

This is appropriate when it is okay for clients to access the entire
contents of the VMO, possibly extending beyond the pages spanned by the
file.

This mode is significantly more efficient than |CLONE_COW| and should be
preferred when file spans the whole VMO or when the VMO's entire content
is safe for clients to read.

kCloneCow

VFS_INTERNAL_SHARING_MODE_COW

The VMO range spanned by the file is cloned on demand, using
copy-on-write semantics to isolate modifications of clients which open
the file in a writable mode.

This is appropriate when clients need to be restricted from accessing
portions of the VMO outside of the range of the file and when file
modifications by clients should not be visible to each other.

Specifies the default behavior when a client asks for the file's underlying VMO, but does not

specify if a duplicate handle or copy-on-write clone is required.

*NOTE*: This does not affect the behavior of requests that specify the required sharing mode.

Requests for a specific sharing mode will be fulfilled as requested.

Defined at line 39 of file ../../sdk/lib/vfs/cpp/vmo_file.h