EFI_GET_VARIABLE(3)

💖 EFI_GET_VARIABLE 💖

okay bestie, so this is the EFI_GET_VARIABLE(3) page from the Library Functions Manual — it's all about manipulating UEFI variables and it's genuinely iconic. grab a boba, we're doing this 🧋✨

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✨ NAME ✨

efi_variables_supported, efi_del_variable, efi_get_variable, efi_get_variable_attributes, efi_get_variable_size, efi_set_variable — manipulate UEFI variables 🦋

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🌸 SYNOPSIS 🌸

#include <efivar.h>

int efi_variables_supported(void);
int efi_del_variable(efi_guid_t guid, const char *name);

int efi_get_variable(efi_guid_t guid, const char *name,
                     void **data, ssize_t *data_size,
                     uint32_t *attributes);

int efi_get_variable_attributes(efi_guid_t guid, const char *name,
                                uint32_t *attributes);

int efi_get_variable_exists(efi_guid_t guid, const char *name);

int efi_get_variable_size(efi_guid_t guid, const char *name,
                          size_t *size);

int efi_append_variable(efi_guid_t guid, const char *name,
                     void *data, size_t data_size,
                     uint32_t attributes);

int efi_set_variable(efi_guid_t guid, const char *name,
                     void *data, size_t data_size,
                     uint32_t attributes, mode_t mode);

int efi_get_next_variable_name(efi_guid_t **guid, char **name);

int efi_str_to_guid(const char *s, efi_guid_t *guid);

int efi_guid_to_str(const efi_guid_t *guid, char **sp);

int efi_name_to_guid(const char *name, efi_guid_t *guid);

int efi_id_guid_to_guid(const char *id_guid, efi_guid_t *guid);

int efi_guid_to_name(efi_guid_t *guid, char **name);

int efi_guid_to_id_guid(efi_guid_t *guid, char **id_guid);

int efi_guid_to_symbol(efi_guid_t *guid, char **symbol);
int efi_symbol_to_guid(const char *symbol, efi_guid_t *guid);

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🎀 DESCRIPTION 🎀

okay so here's the whole cast, one by one, no skips 💅

efi_variables_supported() — tests if the UEFI variable facility is supported on the current machine. vibe check for your hardware, basically.

efi_del_variable() — deletes the variable specified by guid and name. gone. bye. 💀

efi_get_variable() — gets the variable specified by guid and name. the value lands in data, its size in data_size, and its attributes are stored in attributes. the whole package deal 📦

efi_get_variable_attributes() — gets attributes for the variable specified by guid and name. just the attributes, nothing else, she's focused.

efi_get_variable_exists() — gets if the variable specified by guid and name exists. yes/no moment fr.

efi_get_variable_size() — gets the size of the data for the variable specified by guid and name.

efi_append_variable() — appends data of size size to the variable specified by guid and name. adding on, not replacing 👑

efi_set_variable() — sets the variable specified by guid and name, and sets the file mode to mode, subject to umask. note that the mode will not persist across a reboot, and that the permissions only apply if on systems using efivarfs. so like, don't get attached to those perms 😭

efi_get_next_variable_name() — iterates across the currently extant variables, passing back a guid and name. it's giving "one at a time, bestie".

efi_str_to_guid() — parses a UEFI GUID from string form to an efi_guid_t the caller provides.

efi_guid_to_str() — creates a string representation of a UEFI GUID. if sp is NULL, it returns how big the string would be. if sp is not NULL but *sp is NULL, it allocates a string and returns it with. it is the caller's responsibility to free this string. if sp is not NULL and *sp is not NULL, efi_guid_to_str() assumes there is an allocation of suitable size and uses it. three modes, main character energy 🌈

efi_name_to_guid() — translates from a well known name to an efi_guid_t the caller provides.

efi_guid_to_name() — translates from an efi_guid_t to a well known name. if the supplied GUID does not have a well known name, this function is equivalent to efi_guid_to_str().

efi_guid_to_id_guid() — translates from an efi_guid_t to an {ID GUID}. if the supplied GUID has a well known name, the {ID GUID} will be of the form "{name_here}". if not, it will be of the form "{66b2af1c-6211-4082-95cb-9f73a4795a7e}". bestie that's a literal UUID in the manpage, keep it forever 💜

efi_id_guid_to_guid() — translates from an {ID GUID} to an efi_guid_t the caller provides.

efi_guid_to_symbol() — translates from an efi_guid_t to a unique (within libefivar) C-style symbol name. these symbol names are useful for printing as a unique, easily parsed identifier, and are also provide by the library and its header files.

efi_symbol_to_guid() — translates from a libefivar efi_guid_$FOO symbol name to an efi_guid_t the caller provides.

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⭐ RETURN VALUE ⭐

efi_variables_supported() returns true if variables are supported on the running hardware, and false if they are not.

efi_get_next_variable_name() returns 0 when iteration has completed, 1 when iteration has not completed, and -1 on error. in the event of an error, errno(3) is set appropriately.

efi_del_variable(), efi_get_variable(), efi_get_variable_attributes(), efi_get_variable_exists(), efi_get_variable_size(), efi_append_variable(), efi_set_variable(), efi_str_to_guid(), efi_guid_to_str(), efi_name_to_guid(), and efi_guid_to_name() return negative on error and zero on success.

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👑 AUTHORS 👑

Peter Jones <pjones@redhat.com> — shoutout to the author, we love a legend 🫶

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that's the whole page bestie, no notes, you ate that 💅✨

okay so the sign-off: this is from EFI_GET_VARIABLE(3) in the Library Functions Manual, dated Thu Aug 20 2012. vintage but still serving. mwah 💖🎀🦋