Add support for reading symlinks

libc/CMakeLists.txt

@@ -133,6 +133,8 @@ add_library(
     ${PROJECT_SOURCE_DIR}/src/unistd/kill.c
     ${PROJECT_SOURCE_DIR}/src/unistd/signal.c
     ${PROJECT_SOURCE_DIR}/src/unistd/interval.c
+    ${PROJECT_SOURCE_DIR}/src/unistd/symlink.c
+    ${PROJECT_SOURCE_DIR}/src/unistd/readlink.c
     ${PROJECT_SOURCE_DIR}/src/libc_start.c
     ${PROJECT_SOURCE_DIR}/src/crt0.S
 )

libc/inc/limits.h

@@ -53,5 +53,8 @@
 /// Maximum number of characters in a path name.
 #define PATH_MAX 4096
 
+/// Maximum length of arguments provided to exec function.
+#define ARG_MAX 256
+
 /// Maximum pid number.
 #define PID_MAX_LIMIT 32768

libc/inc/sys/unistd.h

@@ -60,6 +60,13 @@ int unlink(const char *path);
 /// @return 0 on success, a negative number if fails and errno is set.
 int symlink(const char *linkname, const char *path);
 
+/// @brief Read the symbolic link, if present.
+/// @param file the file for which we want to read the symbolic link information.
+/// @param buffer the buffer where we will store the symbolic link path.
+/// @param bufsize the size of the buffer.
+/// @return The number of read characters on success, -1 otherwise and errno is set to indicate the error.
+int readlink(const char *path, char *buffer, size_t bufsize);
+
 /// @brief Wrapper for exit system call.
 /// @param status The exit status.
 extern void exit(int status);

libc/src/grp.c

@@ -18,30 +18,31 @@ static int __fd = -1;
 /// @brief It parses the line (as string) and saves its content inside the
 /// group_t structure.
 /// @param grp the struct where we store the information.
-/// @param buf the buffer from which we extract the information.
+/// @param buf the line from which we extract the information.
 static inline void __parse_line(group_t *grp, char *buf)
 {
     assert(grp && "Received null grp!");
     char *token;
     // Parse the group name.
-    if ((token = strtok(buf, ":")) != NULL) {
+    token = strtok(buf, ":");
+    if (token != NULL) {
         grp->gr_name = token;
     }
     // Parse the group passwd.
-    if ((token = strtok(NULL, ":")) != NULL) {
+    token = strtok(NULL, ":");
+    if (token != NULL) {
         grp->gr_passwd = token;
     }
     // Parse the group id.
-    if ((token = strtok(NULL, ":")) != NULL) {
+    token = strtok(NULL, ":");
+    if (token != NULL) {
         grp->gr_gid = atoi(token);
     }
-
     size_t found_users = 0;
     while ((token = strtok(NULL, ",\n\0")) != NULL && found_users < MAX_MEMBERS_PER_GROUP) {
         grp->gr_mem[found_users] = token;
         found_users += 1;
     }
-
     // Null terminate array
     grp->gr_mem[found_users] = "\0";
 }
@@ -52,8 +53,8 @@ static inline void __parse_line(group_t *grp, char *buf)
 /// @param buflen the length of the buffer.
 /// @param name the name we are looking for.
 /// @param gid the group id we must match.
-/// @return a pointer to the filled input buffer on success, NULL on failure.
-static inline char *__search_entry(int fd, char *buf, int buflen, const char *name, gid_t gid)
+/// @return 1 on success, 0 on failure.
+static inline int __search_entry(int fd, char *buf, size_t buflen, const char *name, gid_t gid)
 {
     int ret;
     char c;
@@ -65,7 +66,7 @@ static inline char *__search_entry(int fd, char *buf, int buflen, const char *na
         }
         if (pos >= buflen) {
             errno = ERANGE;
-            return NULL;
+            return 0;
         }
         // If we have found a newline or the EOF, parse the entry.
         if ((c == '\n') || (ret == EOF)) {
@@ -74,7 +75,7 @@ static inline char *__search_entry(int fd, char *buf, int buflen, const char *na
             // Check the entry.
             if (name) {
                 if (strncmp(buf, name, strlen(name)) == 0) {
-                    return buf;
+                    return 1;
                 }
             } else {
                 int gid_start = -1, col_count = 0;
@@ -91,7 +92,7 @@ static inline char *__search_entry(int fd, char *buf, int buflen, const char *na
                     int found_gid = atoi(&buf[gid_start]);
                     // Check the gid.
                     if (found_gid == gid) {
-                        return buf;
+                        return 1;
                     }
                 }
             }
@@ -106,7 +107,7 @@ static inline char *__search_entry(int fd, char *buf, int buflen, const char *na
         }
     }
     errno = ENOENT;
-    return NULL;
+    return 0;
 }
 
 group_t *getgrgid(gid_t gid)
@@ -148,12 +149,11 @@ int getgrgid_r(gid_t gid, group_t *group, char *buf, size_t buflen, group_t **re
         return 0;
     }
 
-    char *entry = __search_entry(fd, buf, buflen, NULL, gid);
-    if (entry != NULL) {
+    if (__search_entry(fd, buf, buflen, NULL, gid)) {
         // Close the file.
         close(fd);
         // Parse the line.
-        __parse_line(group, entry);
+        __parse_line(group, buf);
         // Return success.
         return 1;
     }
@@ -173,12 +173,11 @@ int getgrnam_r(const char *name, group_t *group, char *buf, size_t buflen, group
         return 0;
     }
 
-    char *entry = __search_entry(fd, buf, buflen, name, 0);
-    if (entry != NULL) {
+    if (__search_entry(fd, buf, buflen, name, 0)) {
         // Close the file.
         close(fd);
         // Parse the line.
-        __parse_line(group, entry);
+        __parse_line(group, buf);
         // Return success.
         return 1;
     }

libc/src/unistd/readlink.c

@@ -0,0 +1,10 @@
+/// @file readlink.c
+/// @brief
+/// @copyright (c) 2014-2023 This file is distributed under the MIT License.
+/// See LICENSE.md for details.
+
+#include "sys/unistd.h"
+#include "sys/errno.h"
+#include "system/syscall_types.h"
+
+_syscall3(int, readlink, const char *, path, char *, buffer, size_t, bufsize)

libc/src/unistd/symlink.c

@@ -1,4 +1,4 @@
-/// @file unlink.c
+/// @file symlink.c
 /// @brief
 /// @copyright (c) 2014-2023 This file is distributed under the MIT License.
 /// See LICENSE.md for details.