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authorLennart Poettering <lennart@poettering.net>2018-10-25 21:27:00 +0200
committerSven Eden <sven.eden@prydeworx.com>2018-10-29 10:18:40 +0100
commit85f97ad9e8578b5a9c2de75b7263bd67719a7fea (patch)
tree443278994056ca03ad2e43b8192d191705f8abf5
parent8894c11397f3b2a22cf163f1da9708bba30e4933 (diff)
fd-util: optimize fd_get_path() a bit
journald calls fd_get_path() a lot (it probably shouldn't, there's some room for improvement there, but I'll leave that for another time), hence it's worth optimizing the call a bit, in particular as it's easy. Previously we'd open the dir /proc/self/fd/ first, before reading the symlink inside it. This means the whole function requires three system calls: open(), readlinkat(), close(). The reason for doing it this way is to distinguish the case when we see ENOENT because /proc is not mounted and the case when the fd doesn't exist. With this change we'll directly go for the readlink(), and only if that fails do an access() to see if /proc is mounted at all. This optimizes the common case (where the fd is valid and /proc mounted), in favour of the uncommon case (where the fd doesn#t exist or /proc is not mounted). (cherry picked from commit f267719c389de57ceda433f6288a505e7eeb2f8f)
-rw-r--r--src/basic/fd-util.c24
1 files changed, 12 insertions, 12 deletions
diff --git a/src/basic/fd-util.c b/src/basic/fd-util.c
index 122b59a..229b4a8 100644
--- a/src/basic/fd-util.c
+++ b/src/basic/fd-util.c
@@ -357,22 +357,22 @@ bool fdname_is_valid(const char *s) {
#endif // 0
int fd_get_path(int fd, char **ret) {
- _cleanup_close_ int dir = -1;
- char fdname[DECIMAL_STR_MAX(int)];
+ char procfs_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
int r;
- dir = open("/proc/self/fd/", O_CLOEXEC | O_DIRECTORY | O_PATH);
- if (dir < 0)
- /* /proc is not available or not set up properly, we're most likely
- * in some chroot environment. */
- return errno == ENOENT ? -EOPNOTSUPP : -errno;
+ xsprintf(procfs_path, "/proc/self/fd/%i", fd);
+ r = readlink_malloc(procfs_path, ret);
+ if (r == -ENOENT) {
+ /* ENOENT can mean two things: that the fd does not exist or that /proc is not mounted. Let's make
+ * things debuggable and distuingish the two. */
- xsprintf(fdname, "%i", fd);
+ if (access("/proc/self/fd/", F_OK) < 0)
+ /* /proc is not available or not set up properly, we're most likely in some chroot
+ * environment. */
+ return errno == ENOENT ? -EOPNOTSUPP : -errno;
- r = readlinkat_malloc(dir, fdname, ret);
- if (r == -ENOENT)
- /* If the file doesn't exist the fd is invalid */
- return -EBADF;
+ return -EBADF; /* The directory exists, hence it's the fd that doesn't. */
+ }
return r;
}