LLAPI\_LAYOUT\_GET\_BY\_FD(3) Lustre Library Functions LLAPI\_LAYOUT\_GET\_BY\_FD(3) # [NAME](#NAME) llapi\_layout\_get\_by\_fd, llapi\_layout\_get\_by\_fid, llapi\_layout\_get\_by\_path, llapi\_layout\_get\_by\_xattr, - obtain the layout of a Lustre file # [SYNOPSIS](#SYNOPSIS) ``` #include ``` ``` struct llapi_layout *llapi_layout_get_by_fd(int fd, enum llapi_layout_get_flags flags); ``` ``` struct llapi_layout *llapi_layout_get_by_fid(const char *lustre_path, const struct lu_fid *fid, enum llapi_layout_get_flags flags); ``` ``` struct llapi_layout *llapi_layout_get_by_path(const char *path, enum llapi_layout_get_flags flags); ``` ``` struct llapi_layout *llapi_layout_get_by_xattr(void *lov_xattr, ssize_t lov_xattr_size, enum llapi_layout_get_flags flags); ``` # [DESCRIPTION](#DESCRIPTION) The functions **llapi\_layout\_get\_by\_xattr()**, **llapi\_layout\_get\_by\_fd()**, **llapi\_layout\_get\_by\_fid()**, and **llapi\_layout\_get\_by\_path()** return a pointer to a newly-allocated **struct llapi\_layout** containing the layout information for the file referenced by *lov\_xattr*, *fd*, *fid*, or *path*, respectively. The **struct llapi\_layout** is an opaque entity containing the layout information for a file in a Lustre filesystem. Its internal structure should not be directly accessed by an application. See [**llapi\_layout**(7)](/man/enterprise-packages/lustre/llapi_layout.7). The pointer should be freed with **llapi\_layout\_free()** when it is no longer needed. For **llapi\_layout\_get\_by\_xattr()**, *lov\_xattr* is a Lustre layout extended attribute (LOV EA) from a file or directory in a Lustre filesystem. The *lov\_xattr* should be the raw xattr without being byte-swapped, since this function will swap it to the local machine endianness properly. For **llapi\_layout\_get\_by\_fd()**, *fd* is a valid open file descriptor for a file or directory in a Lustre filesystem. For **llapi\_layout\_get\_by\_fid()**, *lustre\_path* identifies the Lustre filesystem containing the file represented by *fid*. It is typically the filesystem root directory, but may also be any path beneath the root. Use the function [**llapi\_path2fid**(3)](/man/enterprise-packages/lustre/llapi_path2fid.3) to obtain a **struct lu\_fid** associated with a given path. The function **llapi\_layout\_get\_by\_path()** accepts a *path* argument that names a file or directory in a Lustre filesystem. Zero or more flags may be bitwise-or'd together in *flags* to control how a layout is retrieved. Currently **llapi\_layout\_get\_by\_fd()** and **llapi\_layout\_get\_by\_fid()** do not accept any values for *flags*, while **llapi\_layout\_get\_by\_path()** accepts only one flag as follows: [**LLAPI\_LAYOUT\_GET\_EXPECTED**](#LLAPI_LAYOUT_GET_EXPECTED) Unspecified attribute values are replaced by the literal default values that will be assigned when the file is created or first written to. A default value is inherited from the parent directory if the attribute is specified there, otherwise it is inherited from the filesystem root. This flag is only recognized by **llapi\_layout\_get\_by\_path()**. Unspecified attributes may belong to directories and never-written-to files. By default, layouts report the abstract value **LLAPI\_LAYOUT\_DEFAULT** to indicate an unspecified attribute. Use **LLAPI\_LAYOUT\_GET\_EXPECTED** to discover the expected literal values for new files in a given directory. Do not use it if you need to distinguish between specified and unspecified attributes. The flag has no effect if *path* names a file or directory with a fully specified layout. For concreteness, consider a Lustre filesystem with a default stripe size of 1048576 and a default stripe count of 1. A user sets the stripe count for directory D to 2 (thus overriding the filesystem-wide default) but leaves the stripe size unspecified. Newly created files in D inherit a stripe count of 2 from D and a stripe size of 1048576 from the filesystem default. The layout of D returned by **llapi\_layout\_get\_by\_path(D, 0)** has the abstract stripe size value **LLAPI\_LAYOUT\_DEFAULT**, since stripe size is unspecified, while **llapi\_layout\_get\_by\_path(D, LLAPI\_LAYOUT\_GET\_EXPECTED)** reports the literal value 1048576. Both forms report a stripe count of 2, since that attribute is specified. Valid arguments for *flags* with **llapi\_layout\_get\_by\_xattr()** are: [**LLAPI\_LAYOUT\_GET\_CHECK**](#LLAPI_LAYOUT_GET_CHECK) If the **LLAPI\_LAYOUT\_GET\_CHECK** flag is set, this function will check whether the objects count in lum is consistent with the stripe count in lum. This check only apply to regular files, so it should not be passed if the xattr is a default layout from a directory. [**LLAPI\_LAYOUT\_GET\_COPY**](#LLAPI_LAYOUT_GET_COPY) If the **LLAPI\_LAYOUT\_GET\_COPY** flag is set, this function will use a temporary buffer for byte swapping when necessary, leaving *lov\_xattr* unmodified. Otherwise, the byte swapping will be done to the fields of the *lov\_xattr* buffer directly. # [RETURN VALUES](#RETURN_VALUES) These functions return a valid pointer on success or **NULL** on failure with **errno** set to an appropriate error code. # [ERRORS](#ERRORS) [**ENOMEM**](#ENOMEM) Insufficient storage space is available. [**ENOTTY**](#ENOTTY) File does not reside on a Lustre filesystem. [**ENOENT**](#ENOENT) *path* does not exist. [**EINVAL**](#EINVAL) An invalid argument was specified. [**EINTR**](#EINTR) The kernel returned less than the expected amount of data. # [NOTES](#NOTES) When using these functions to copy an existing file's layout to create a new file with [**llapi\_layout\_file\_open (3)**](/man/enterprise-packages/lustre/llapi_layout_file_open.3) for mirroring, migration, or as the template for a new file, [**llapi\_layout\_ost\_index\_reset**(3)](/man/enterprise-packages/lustre/llapi_layout_ost_index_reset.3) should be called to reset the OST index values for each component, so that the file copy is not created on exactly the same OSTs as the original file. # [AVAILABILITY](#AVAILABILITY) **llapi\_layout\_get\_by\_fd(),** **llapi\_layout\_get\_by\_fid(),** **llapi\_layout\_get\_by\_path()** and **llapi\_layout\_get\_by\_xattr()** are part of the [**lustre**(7)](/man/enterprise-packages/lustre/lustre.7) user application interface library since release 2.7.0 # [SEE ALSO](#SEE_ALSO) [**llapi\_layout\_file\_open**(3)](/man/enterprise-packages/lustre/llapi_layout_file_open.3), [**llapi\_layout\_ost\_index\_reset**(3)](/man/enterprise-packages/lustre/llapi_layout_ost_index_reset.3), [**llapi\_path2fid**(3)](/man/enterprise-packages/lustre/llapi_path2fid.3), [**llapi\_layout**(7)](/man/enterprise-packages/lustre/llapi_layout.7), [**lustreapi**(7)](/man/enterprise-packages/lustre/lustreapi.7) 2025-03-19 Lustre User API --- Document: llapi_layout_get_by_fd(3) from lustre 2.17.59-r1 (Chainguard OS) Source: https://github.com/lustre/lustre-release