LLAPI\_LAYOUT\_FILE\_OPEN\_VOLATILE(3) Lustre Library Functions LLAPI\_LAYOUT\_FILE\_OPEN\_VOLATILE(3) # [NAME](#NAME) llapi\_layout\_file\_open\_volatile, llapi\_file\_open\_volatile - open new temporary file with layout # [SYNOPSIS](#SYNOPSIS) ``` #include ``` ``` int llapi_layout_file_open_volatile(const char *directory, int mdt_idx, int open_flags, mode_t mode, const struct llapi_layout *layout) ``` ``` int llapi_file_open_volatile(const char *directory, int open_flags) ``` ``` int llapi_file_open_volatile_idx(const char *directory, int mdt_idx, int open_flags) ``` ``` int llapi_file_open_volatile_param(const char *directory, int mdt_idx, int open_flags, mode_t mode, const struct llapi_stripe_param *param) ``` # [DESCRIPTION](#DESCRIPTION) The **llapi\_layout\_file\_open\_volatile**() function and its **llapi\_file\_open\_volatile\***() variants open a file handle on a new anonymous, temporary, volatile file on a Lustre filesystem, similar to the Linux kernel [**open**(2)](/man/enterprise-packages/lustre/open.2) **O\_TMPFILE** functionality. The variants allow increasing specificity in the layout of the created file, see [**llapi\_file\_open\_param**(3)](/man/enterprise-packages/lustre/llapi_file_open_param.3) and [**llapi\_layout\_file\_create**(3)](/man/enterprise-packages/lustre/llapi_layout_file_create.3) for details of usage. The created file is not visible in the namespace with [**ls**(1)](/man/enterprise-packages/lustre/ls.1). Once the file is closed, or the owning process dies, the file and its objects are permanently deleted from the filesystem. With no layout or stripe parameters these functions will also work on a non-Lustre filesystem, where the file is created then unlinked, leaving only the file descriptor to access the file. This is not strictly equivalent because there is a small window during which the file is visible to users (provided they have access to the parent *directory*). Given a *layout* or *stripe\_param*, the call instead fails there, since the striping cannot be applied: **ENOTTY** in general, or **ENODEV** when *stripe\_param* names a pool, which is looked up before the filesystem is touched. The *directory* parameter indicates where to create the file on the Lustre filesystem. *mdt\_idx* is the MDT index onto which to create the file. To use a default MDT, set mdt\_idx to -1. *open\_flags* are standard [**open**(2)](/man/enterprise-packages/lustre/open.2) flags, but a read-only access mode is promoted to **O\_RDWR** and **O\_CREAT**, **O\_EXCL** and **O\_NOFOLLOW** are always added: the file has to be created to be returned. *mode* is the same as [**open**(2)](/man/enterprise-packages/lustre/open.2). *layout* and *param* are different structures that describe the striping information. If it is NULL, then the default for the directory is used. **struct llapi\_layout** is an opaque data structure that is allocated by [**llapi\_layout\_alloc**(3)](/man/enterprise-packages/lustre/llapi_layout_alloc.3) and modified with the [**llapi\_layout**(7)](/man/enterprise-packages/lustre/llapi_layout.7) functions. # [RETURN VALUE](#RETURN_VALUE) All variants return an open file descriptor on success, or a negative errno on failure. # [ERRORS](#ERRORS) The negative errno can be, but is not limited to: [**-EINVAL**](#EINVAL) An invalid value was passed. [**-ENOMEM**](#ENOMEM) Not enough memory to allocate a resource. [**-ENAMETOOLONG**](#ENAMETOOLONG) The generated volatile file name does not fit in PATH\_MAX. [**-ENODEV**](#ENODEV) *stripe\_param* names a pool and *directory* is not on a Lustre filesystem. [**-ENOTTY**](#ENOTTY) *layout* is non-NULL and *directory* is not on a Lustre filesystem. # [EXAMPLES](#EXAMPLES) Create volatile file on MDT0002, copy data to it, and swap layouts: ``` #include int main(int argc, char *argv[]) { int fd_src, fd_dst; __u64 dv_src, dv_dst; struct llapi_layout *layout = NULL; int rc; layout = llapi_layout_alloc(); if (!layout) { fprintf(stderr, "%s: layout allocation failed: %s\n", argv[0], strerror(errno)); return errno; } rc = llapi_layout_stripe_count_set(layout, 2); : fd_dst = llapi_layout_file_open_volatile(argv[1], 2, 0, 0644, layout); if (fd_dst < 0) { rc = -fd_dst; fprintf(stderr, "%s: volatile file creation failed: %s\n", argv[0], strerror(rc)); goto out; } fd_src = open(argv[2], O_RDWR); rc = llapi_get_data_version(fd_src, &dv_src, 0); : /* copy data from @fd_src to @fd_dst */ : rc = llapi_get_data_version(fd_src, &dv_dst, LL_DV_RD_FLUSH); : rc = llapi_fswap_layouts(fd_src, fd_dst, dv_src, dv_dst, SWAP_LAYOUTS_CLOSE); if (rc < 0) { fprintf(stderr, "%s: swap layouts failed: %s\n", argv[0], strerror(-rc)); goto out; } out: llapi_layout_free(layout); return rc; } ``` # [AVAILABILITY](#AVAILABILITY) The **llapi\_layout\_file\_open\_volatile()**, **llapi\_file\_open\_volatile()**, **llapi\_file\_open\_volatile\_idx()**, and **llapi\_file\_open\_volatile\_param()** variants are part of the [**lustre**(7)](/man/enterprise-packages/lustre/lustre.7) user application interface library since release 2.18.0. These functions were originally implemented as **llapi\_create\_volatile\_param(),** **llapi\_create\_volatile\_idx(),** and **llapi\_create\_volatile()** in release 2.4.0, but were renamed and deprecated because the **create** name does not accurately reflect that they return an open file descriptor. # [AUTHORS](#AUTHORS) Frank Zago for Cray Inc. # [SEE ALSO](#SEE_ALSO) [**llapi\_file\_open**(3)](/man/enterprise-packages/lustre/llapi_file_open.3), [**llapi\_file\_open\_param**(3)](/man/enterprise-packages/lustre/llapi_file_open_param.3), [**llapi\_file\_open\_pool**(3)](/man/enterprise-packages/lustre/llapi_file_open_pool.3), [**llapi\_fswap\_layouts**(3)](/man/enterprise-packages/lustre/llapi_fswap_layouts.3), [**llapi\_layout\_file\_create**(3)](/man/enterprise-packages/lustre/llapi_layout_file_create.3), [**lustreapi**(7)](/man/enterprise-packages/lustre/lustreapi.7) 2026-08-12 Lustre User API --- Document: llapi_file_open_volatile_param(3) from lustre 2.17.59-r1 (Chainguard OS) Source: https://github.com/lustre/lustre-release