DEBUGINFOD_FIND_*

Section: C Library Functions (3)
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NAME

debuginfod_find_debuginfo - request debuginfo from debuginfod

SYNOPSIS

#include <elfutils/debuginfod.h>

Link with -ldebuginfod.

CONNECTION HANDLE

debuginfod_client *debuginfod_begin(void);
void debuginfod_end(debuginfod_client *client);

LOOKUP FUNCTIONS

int debuginfod_find_debuginfo(debuginfod_client *client,
                              const unsigned char *build_id,
                              int build_id_len,
                              char ** path);
int debuginfod_find_executable(debuginfod_client *client,
                               const unsigned char *build_id,
                               int build_id_len,
                               char ** path);
int debuginfod_find_source(debuginfod_client *client,
                           const unsigned char *build_id,
                           int build_id_len,
                           const char *filename,
                           char ** path);

OPTIONAL FUNCTIONS

typedef int (*debuginfod_progressfn_t)(debuginfod_client *client,
                                       long a, long b);
void debuginfod_set_progressfn(debuginfod_client *client,
                               debuginfod_progressfn_t progressfn);
void debuginfod_set_verbose_fd(debuginfod_client *client,
                               int fd);
void debuginfod_set_user_data(debuginfod_client *client,
                              void *data);
void* debuginfod_get_user_data(debuginfod_client *client);
const char* debuginfod_get_url(debuginfod_client *client);
int debuginfod_add_http_header(debuginfod_client *client,
                               const char* header);

DESCRIPTION

debuginfod_begin() creates a debuginfod_client connection handle that should be used with all other calls. debuginfod_end() should be called on the client handle to release all state and storage when done.

debuginfod_find_debuginfo(), debuginfod_find_executable(), and debuginfod_find_source() query the debuginfod server URLs contained in $DEBUGINFOD_URLS (see below) for the debuginfo, executable or source file with the given build_id. build_id should be a pointer to either a null-terminated, lowercase hex string or a binary blob. If build_id is given as a hex string, build_id_len should be 0. Otherwise build_id_len should be the number of bytes in the binary blob.

debuginfod_find_source() also requires a filename in order to specify a particular source file. filename should be an absolute path that includes the compilation directory of the CU associated with the source file. Relative path names commonly appear in the DWARF file's source directory, but these paths are relative to individual compilation unit AT_comp_dir paths, and yet an executable is made up of multiple CUs. Therefore, to disambiguate, debuginfod expects source queries to prefix relative path names with the CU compilation-directory, followed by a mandatory "/".

Note: the caller may or may not elide ../ or /./ or extraneous /// sorts of path components in the directory names. debuginfod accepts both forms. Specifically, debuginfod canonicalizes path names according to RFC3986 section 5.2.4 (Remove Dot Segments), plus reducing any // to / in the path.

If path is not NULL and the query is successful, path is set to the path of the file in the cache. The caller must free() this value.

The URLs in $DEBUGINFOD_URLS may be queried in parallel. As soon as a debuginfod server begins transferring the target file all of the connections to the other servers are closed.

A client handle should be used from only one thread at a time.

RETURN VALUE

debuginfod_begin returns the debuginfod_client handle to use with all other calls. On error NULL will be returned and errno will be set.

If a find family function is successful, the resulting file is saved to the client cache and a file descriptor to that file is returned. The caller needs to close() this descriptor. Otherwise, a negative error code is returned.

OPTIONAL FUNCTIONS

A small number of optional functions are available to tune or query the operation of the debuginfod client.

PROGRESS CALLBACK

As the debuginfod_find_*() functions may block for seconds or longer, a progress callback function is called periodically, if configured with debuginfod_set_progressfn(). This function sets a new progress callback function (or NULL) for the client handle.

The given callback function is called from the context of each thread that is invoking any of the other lookup functions. It is given two numeric parameters that, if thought of as a numerator a and denominator b, together represent a completion fraction a/b. The denominator may be zero initially, until a quantity such as an exact download size becomes known.

The progress callback function is also the supported way to interrupt the download operation. (The library does not modify or trigger signals.) The progress callback must return 0 to continue the work, or any other value to stop work as soon as possible. Consequently, the debuginfod_find_*() function will likely return with an error, but might still succeed.

VERBOSE OUTPUT

The debuginfod_find_*() functions may use several techniques to retrieve the requested files, through the cache or through one or multiple servers or file URLs. To show how a query is handled the debuginfod_set_verbose_fd() can be used to set a particular file descriptor on which verbose output is given about the query steps and eventual errors encountered.

USER DATA POINTER

A single void * pointer associated with the connection handle may be set any time via debuginfod_set_user_data(), and retrieved via debuginfod_get_user_data(). The value is undefined if unset.

URL

The URL of the current or most recent outgoing download, if known, may be retrieved via debuginfod_get_url() from the progressfn callback, or afterwards. It may be NULL. The resulting string is owned by the library, and must not be modified or freed. The caller should copy it if it is needed beyond the release of the client object.

HTTP HEADER

Before a lookup function is initiated, a client application may add HTTP request headers to future downloads. debuginfod_add_http_header() may be called with strings of the form Header:~value. These strings are copied by the library. A zero return value indicates success, but out-of-memory conditions may result in a non-zero -ENOMEM. If the string is in the wrong form -EINVAL will be returned.

Note that the current debuginfod-client library implementation uses libcurl, but you shouldn't rely on that fact. Don't use this function for replacing any standard headers, except for the User-Agent mentioned below. The only supported usage of this function is for adding an optional header which might or might not be passed through to the server for logging purposes only.

By default, the library adds a descriptive User-Agent: header to outgoing requests. If the client application adds a header with the same name, this default is suppressed.

CACHE

If the query is successful, the debuginfod_find_*() functions save the target file to a local cache. The location of the cache is controlled by the $DEBUGINFOD_CACHE_PATH environment variable (see below). Cleaning of the cache is controlled by the cache_clean_interval_s and max_unused_age_s files, which are found in the $DEBUGINFOD_CACHE_PATH directory. cache_clean_interval_s controls how frequently the cache is traversed for cleaning and max_unused_age_s controls how long a file can go unused (fstat(2) atime) before it's removed from the cache during cleaning. These files should contain only an ASCII decimal integer representing the interval or max unused age in seconds. The default is one day and one week, respectively. Values of zero mean "immediately".

MACROS

DEBUGINFOD_SONAME

Defined to the string that could be passed to dlopen(3) if the library is loaded at runtime, for example

void *debuginfod_so = dlopen(DEBUGINFOD_SONAME, RTLD_LAZY);

SECURITY

debuginfod_find_debuginfo(), debuginfod_find_executable(), and debuginfod_find_source() do not include any particular security features. They trust that the binaries returned by the debuginfod(s) are accurate. Therefore, the list of servers should include only trustworthy ones. If accessed across HTTP rather than HTTPS, the network should be trustworthy. Passing user authentication information through the internal libcurl library is not currently enabled, except for the basic plaintext http[s]://userid:password@hostname/ style. (The debuginfod server does not perform authentication, but a front-end proxy server could.)

ENVIRONMENT VARIABLES

DEBUGINFOD_URLS

This environment variable contains a list of URL prefixes for trusted debuginfod instances. Alternate URL prefixes are separated by space.

DEBUGINFOD_TIMEOUT

This environment variable governs the timeout for each debuginfod HTTP connection. A server that fails to provide at least 100K of data within this many seconds is skipped. The default is 90 seconds. (Zero or negative means "no timeout".)

DEBUGINFOD_PROGRESS

This environment variable governs the default progress function. If set, and if a progressfn is not explicitly set, then the library will configure a default progressfn. This function will append a simple progress message periodically to stderr. The default is no progress function output.

DEBUGINFOD_VERBOSE

This environment variable governs the default file descriptor for verbose output. If set, and if a verbose fd is not explicitly set, then the verbose output will be produced on STDERR_FILENO.

DEBUGINFOD_CACHE_PATH

This environment variable governs the location of the cache where downloaded files are kept. It is cleaned periodically as this program is reexecuted. If XDG_CACHE_HOME is set then $XDG_CACHE_HOME/debuginfod_client is the default location, otherwise $HOME/.cache/debuginfod_client is used.

ERRORS

The following list is not comprehensive. Error codes may also originate from calls to various C Library functions.

EACCESS: Denied access to resource located at the URL.
ECONNREFUSED: Unable to connect to remote host. Also returned when an HTTPS connection couldn't be verified (bad certificate).
ECONNRESET: Unable to either send or receive network data.
EHOSTUNREACH: Unable to resolve remote host.
EINVAL: One or more arguments are incorrectly formatted. build_id may be too long (greater than 256 characters), filename may not be an absolute path or a debuginfod URL is malformed.
EIO: Unable to write data received from server to local file.
EMLINK: Too many HTTP redirects.
ENETUNREACH: Unable to initialize network connection.
ENOENT: Could not find the resource located at URL. Often this error code indicates that a debuginfod server was successfully contacted but the server could not find the target file.
ENOMEM: System is unable to allocate resources.
ENOSYS: $DEBUGINFOD_URLS is not defined.
ETIME: Query failed due to timeout. $DEBUGINFOD_TIMEOUT controls the timeout duration. See debuginfod(8) for more information.

FILES

$HOME/.debuginfod_client_cache: Default cache directory. If XDG_CACHE_HOME is not set then $HOME/.cache/debuginfod_client is used.